Light-emitting device, display device, and electronic device with color conversion layers

ABSTRACT

A light-emitting device, an electronic device, and a display device each consume less power are provided. The light-emitting device includes a first light-emitting element, a second light-emitting element, and a third light-emitting element that share an EL layer. The EL layer includes a layer containing a light-emitting material that emits blue fluorescence and a layer containing a light-emitting material that emits yellow or green phosphorescence. Light emitted from the second light-emitting element enters a color filter layer or a second color conversion layer, and light emitted from the third light-emitting element enters a first color conversion layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application Ser. No. 14/725,068,filed May 29, 2015, now allowed, which claims the benefit of foreignpriority applications filed in Japan as Serial No. 2014-112796 on May30, 2014, and Serial No. 2014-112849 on May 30, 2014, all of which areincorporated by reference.

TECHNICAL FIELD

One embodiment of the present invention relates to a light-emittingdevice, a display device, a display module, a lighting module, anelectronic device, and a lighting device. Note that one embodiment ofthe present invention is not limited to the above technical field. Thetechnical field of one embodiment of the invention disclosed in thisspecification and the like relates to an object, a method, or amanufacturing method. In addition, one embodiment of the presentinvention relates to a process, a machine, manufacture, or a compositionof matter. Specifically, examples of the technical field of oneembodiment of the present invention disclosed in this specificationinclude a semiconductor device, a display device, a liquid crystaldisplay device, a light-emitting device, a lighting device, a powerstorage device, a storage device, a method for driving any of them, anda method for manufacturing any of them.

BACKGROUND ART

As next-generation lighting devices or display devices, devices usinglight-emitting elements (organic EL elements) in which organic compoundsare used as light-emitting substances have been developed andcommercialized because of their potential for thinness, lightness, highspeed response to input signals, low power consumption, and the like.

In an organic EL element, voltage application between electrodes,between which a light-emitting layer is interposed, causes recombinationof electrons and holes injected from the electrodes, which brings alight-emitting substance (an organic compound) into an excited state,and the return from the excited state to the ground state is accompaniedby light emission. Since the spectrum of light emitted from alight-emitting substance depends on the light-emitting substance, use ofdifferent types of organic compounds as light-emitting substances makesit possible to obtain light-emitting elements that exhibit variouscolors.

For display devices that are expected to display images, such asdisplays, at least three-color light, i.e., red light, green light, andblue light are necessary to reproduce full-color images. For highercolor reproducibility and higher quality of the display images, thecolor purity of emitted light is increased with the use of a microcavitystructure or a color filter.

Furthermore, a variety of measures, such as changing molecularstructures of light-emitting materials to be used and adjusting thematerials or the compositions of materials of a light-emitting elementand the structure of a light-emitting element, are taken to reduce powerconsumption.

REFERENCE Patent Document

[Patent Document 1] Japanese Published Patent Application No.2009-129586

DISCLOSURE OF INVENTION

An object of one embodiment of the present invention is to provide anovel light-emitting device. Another object of one embodiment of thepresent invention is to provide a light-emitting device with low powerconsumption. Another object of one embodiment of the present inventionis to provide an electronic device and a display device each with lowpower consumption.

It is only necessary that at least one of the above-described objects beachieved in one embodiment of the present invention.

In one embodiment of the present invention, the object can be achievedby obtaining a desired emission color with the use of a color conversionlayer in a light-emitting device using an organic compound as alight-emitting material.

One embodiment of the present invention is a light-emitting device withlight-emitting elements using an organic compound. The light-emittingdevice includes at least a first light-emitting element, a secondlight-emitting element, and a third light-emitting element. The firstlight-emitting element, the second light-emitting element, and the thirdlight-emitting element share an EL layer. The EL layer includes a layercontaining a light-emitting material that emits blue fluorescence and alayer containing a light-emitting material that emits greenphosphorescence. Light emitted from the third light-emitting elemententers a first color conversion layer.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which light emitted from thefirst light-emitting element is extracted from the light-emitting devicethrough a color filter that transmits blue light.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which light emitted from thesecond light-emitting element is extracted from the light-emittingdevice through a color filter that transmits green light.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which light emitted from thesecond light-emitting element enters a second color conversion layerthat emits green light.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the first light-emittingelement, the second light-emitting element, and the third light-emittingelement are tandem light-emitting elements.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the layer containing thelight-emitting material that emits blue fluorescence and the layercontaining the light-emitting material that emits green phosphorescenceare adjacent to each other in the first light-emitting element, thesecond light-emitting element, and the third light-emitting element.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the PL quantum yield ofat least one of the first color conversion layer and the second colorconversion layer is higher than 40%.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the PL quantum yield ofat least one of the first color conversion layer and the second colorconversion layer is higher than 53.3%.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the PL quantum yield ofat least one of the first color conversion layer and the second colorconversion layer is higher than 66%.

Another embodiment of the present invention is a light-emitting devicewith a light-emitting element using an organic compound, which has thefollowing characteristics. The light-emitting device includes at least afirst light-emitting element, a second light-emitting element, and athird light-emitting element. The first light-emitting element includesan EL layer with a first structure. The second light-emitting elementand the third light-emitting element include an EL layer with a secondstructure. The EL layer with the first structure includes a layercontaining a light-emitting material that emits blue fluorescence and alayer containing a light-emitting material that emits greenphosphorescence. The EL layer with the second structure includes thelayer containing the light-emitting material that emits greenphosphorescence. Light emitted from the third light-emitting elemententers a first color conversion layer.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the layer containing thelight-emitting material that emits blue fluorescence is closer to ananode than the layer containing the light-emitting material that emitsgreen phosphorescence is, and the layer containing the light-emittingmaterial that emits blue fluorescence and the layer containing thelight-emitting material that emits green phosphorescence each have anelectron-transport property higher than a hole-transport property.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the layer containing thelight-emitting material that emits blue fluorescence is closer to acathode than the layer containing the light-emitting material that emitsgreen phosphorescence is, and the layer containing the light-emittingmaterial that emits blue fluorescence and the layer containing thelight-emitting material that emits green phosphorescence each have ahole-transport property higher than an electron-transport property.

Another embodiment of the present invention is a light-emitting devicewith a light-emitting element using an organic compound, which has thefollowing characteristics. The light-emitting device includes at least afirst light-emitting element, a second light-emitting element, and athird light-emitting element. The first light-emitting element includesan EL layer with a third structure. The second light-emitting elementand the third light-emitting element include an EL layer with a fourthstructure. The EL layer with the fourth structure includes a layercontaining a light-emitting material that emits blue fluorescence and alayer containing a light-emitting material that emits greenphosphorescence. The EL layer with the third structure includes thelayer containing the light-emitting material that emits bluefluorescence. Light emitted from the third light-emitting element entersa first color conversion layer.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the layer containing thelight-emitting material that emits blue fluorescence is closer to ananode than the layer containing the light-emitting material that emitsgreen phosphorescence is, and the layer containing the light-emittingmaterial that emits blue fluorescence and the layer containing thelight-emitting material that emits green phosphorescence each have ahole-transport property higher than an electron-transport property.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the layer containing thelight-emitting material that emits blue fluorescence is closer to acathode than the layer containing the light-emitting material that emitsgreen phosphorescence is, and the layer containing the light-emittingmaterial that emits blue fluorescence and the layer containing thelight-emitting material that emits green phosphorescence each have anelectron-transport property higher than a hole-transport property.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the PL quantum yield ofthe first color conversion layer is higher than 50%.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the layer containing thelight-emitting material that emits green phosphorescence furthercontains a first organic compound and a second organic compound, and thefirst organic compound and the second organic compound form an exciplex.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which an emission spectrum ofthe exciplex overlaps with an absorption band on the longest wavelengthside of the light-emitting material that emits green phosphorescence.

Another embodiment of the present invention is a light-emitting devicewith a light-emitting element using an organic compound, which has thefollowing characteristics. The light-emitting device includes at least afirst light-emitting element, a second light-emitting element, and athird light-emitting element. The first light-emitting element, thesecond light-emitting element, and the third light-emitting elementshare an EL layer. The EL layer includes a light-emitting material thatemits blue fluorescence and a light emitting material that emits yellowphosphorescence. Light emitted from the second light-emitting elemententers a second color conversion layer, and light emitted from the thirdlight-emitting element enters a first color conversion layer.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which light emitted from thefirst light-emitting element is extracted from the light-emitting devicethrough a color filter that transmits blue light.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the second light-emittingelement includes a microcavity structure that amplifies blue light.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the first light-emittingelement, the second light-emitting element, and the third light-emittingelement are tandem light-emitting elements.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the layer containing thelight-emitting material that emits blue fluorescence and the layercontaining the light-emitting material that emits yellow phosphorescenceare adjacent to each other in the first light-emitting element, thesecond light-emitting element, and the third light-emitting element.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the PL quantum yield ofthe first color conversion layer is higher than 40%.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the PL quantum yield ofthe first color conversion layer is higher than 50%.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the PL quantum yield ofthe first color conversion layer is higher than 53.3%.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the PL quantum yield ofthe first color conversion layer is higher than 66%.

Another embodiment of the present invention is a light-emitting devicewith a light-emitting element using an organic compound, which has thefollowing characteristics. The light-emitting device includes at least afirst light-emitting element, a second light-emitting element, and athird light-emitting element. The first light-emitting element and thesecond light-emitting element include an EL layer with a fifthstructure. The third light-emitting element includes an EL layer with asixth structure. The EL layer with the fifth structure includes a layercontaining a light-emitting material that emits blue fluorescence and alayer containing a light-emitting material that emits yellowphosphorescence. The EL layer with the sixth structure includes thelayer containing the light-emitting material that emits yellowphosphorescence. Light emitted from the second light-emitting elemententers a second color conversion layer, and light emitted from the thirdlight-emitting element enters a first color conversion layer.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the layer containing thelight-emitting material that emits blue fluorescence is closer to ananode than the layer containing the light-emitting material that emitsyellow phosphorescence is, and the layer containing the light-emittingmaterial that emits blue fluorescence and the layer containing thelight-emitting material that emits yellow phosphorescence each have anelectron-transport property higher than a hole-transport property.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the layer containing thelight-emitting material that emits blue fluorescence is closer to acathode than the layer containing the light-emitting material that emitsyellow phosphorescence is, and the layer containing the light-emittingmaterial that emits blue fluorescence and the layer containing thelight-emitting material that emits yellow phosphorescence each have ahole-transport property higher than an electron-transport property.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, further including a fourthlight-emitting element, in which light emitted from the fourthlight-emitting element is extracted from the light-emitting devicethrough a color filter that transmits yellow light.

Another embodiment of the present invention is a light-emitting devicewith a light-emitting element using an organic compound, which has thefollowing characteristics. The light-emitting device includes at least afirst light-emitting element, a second light-emitting element, and athird light-emitting element. The first light-emitting element and thesecond light-emitting element include an EL layer with a seventhstructure, and the third light-emitting element includes an EL layerwith an eighth structure. The EL layer with the eighth structureincludes a layer containing a light-emitting material that emits bluefluorescence and a layer containing a light-emitting material that emitsyellow phosphorescence. The EL layer with the seventh structure includesthe layer containing the light-emitting material that emits bluefluorescence. Light emitted from the second light-emitting elemententers a second color conversion layer, and light emitted from the thirdlight-emitting element enters a first color conversion layer.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the layer containing thelight-emitting material that emits blue fluorescence is closer to ananode than the layer containing the light-emitting material that emitsyellow phosphorescence is, and the layer containing the light-emittingmaterial that emits blue fluorescence and the layer containing thelight-emitting material that emits yellow phosphorescence each have ahole-transport property higher than an electron-transport property.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the layer containing thelight-emitting material that emits blue fluorescence is closer to acathode than the layer containing the light-emitting material that emitsyellow phosphorescence is, and the layer containing the light-emittingmaterial that emits blue fluorescence and the layer containing thelight-emitting material that emits yellow phosphorescence each have anelectron-transport property higher than a hole-transport property.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, further including a fourthlight-emitting element including the EL layer with the fourth structure,in which light emitted from the fourth light-emitting element isextracted from the light-emitting device through a color filter thattransmits yellow light.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the PL quantum yield ofthe first color conversion layer is greater than or equal to 50%.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the second colorconversion layer emits green light.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the layer containing thelight-emitting material that emits yellow phosphorescence furthercontains a first organic compound and a second organic compound, and thefirst organic compound and the second organic compound form an exciplex.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which an emission spectrum ofthe exciplex overlaps with an absorption band on the longest wavelengthside of the light-emitting material that emits yellow phosphorescence.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the first colorconversion layer emits red light.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure further including a fourthlight-emitting element, in which light emitted from the fourthlight-emitting element enters a third color conversion layer, and thethird color conversion layer emits yellow light.

Another embodiment of the present invention is the light-emitting devicehaving the above-described structure, in which the first colorconversion layer includes quantum dots.

Another embodiment of the present invention is an electronic deviceincluding the light-emitting device having the above-described structureand at least one of a sensor, an operation button, a speaker, and amicrophone.

According to one embodiment of the present invention, a novellight-emitting device can be provided. According to one embodiment ofthe present invention, a light-emitting device with low powerconsumption can be provided. According to another embodiment of thepresent invention, a display device and an electronic device each withlow power consumption can be provided.

It is only necessary that at least one of the effects from the aboveobjects be achieved in one embodiment of the present invention.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1D are conceptual diagrams of light-emitting devices;

FIGS. 2A to 2D are conceptual diagrams of light-emitting devices;

FIGS. 3A to 3D are conceptual diagrams of light-emitting devices;

FIGS. 4A to 4D are conceptual diagrams of light-emitting devices;

FIGS. 5A to 5C are conceptual diagrams of light-emitting elements;

FIGS. 6A and 6B are conceptual diagrams of an active matrixlight-emitting device;

FIGS. 7A and 7B are conceptual diagrams of active matrix light-emittingdevices;

FIG. 8 is a conceptual diagram of an active matrix light-emittingdevice;

FIGS. 9A and 9B are conceptual diagrams of a passive matrixlight-emitting device;

FIGS. 10A, 10B1, 10B2, 10C, and 10D illustrate electronic devices;

FIG. 11 illustrates in-vehicle display devices and lighting devices; and

FIGS. 12A to 12C illustrate an electronic device.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be explained in detail belowwith reference to the drawings. Note that the present invention is notlimited to the description below, and it is easily understood by thoseskilled in the art that various changes and modifications can be madewithout departing from the spirit and scope of the present invention.Accordingly, the present invention should not be interpreted as beinglimited to the content of the embodiments below. Drawings forillustrating embodiments of the present invention are shown in FIGS. 1Ato 1D, FIGS. 2A to 2D, FIGS. 3A to 3D, and FIGS. 4A to 4D.

<Conversion from Tandem Element Utilizing Blue Fluorescence and GreenPhosphorescence>

FIG. 1A shows a light-emitting device of one embodiment of the presentinvention using a tandem element utilizing blue fluorescence and greenphosphorescence. The light-emitting device includes at least a firstlight-emitting element, a second light-emitting element, and a thirdlight-emitting element that are provided over a substrate 100. The firstto third light-emitting elements share an EL layer 103 and a secondelectrode 104, and each have a different first electrode. The firstlight-emitting element, the second light-emitting element, and the thirdlight-emitting element include a first electrode 102B, a first electrode102G, and a first electrode 102R, respectively. A sealing substrate 101is provided with a black matrix 105, a color filter 107B, a color filter107G, and a color conversion layer 106R. The color filter 107B transmitsblue light, and the color filter 107G transmits green light. The colorconversion layer 106R contains a color conversion substance that emitsred light.

In FIG. 1A, the EL layer 103 has a tandem structure, a typical exampleof which is shown in FIG. 5A. The tandem structure refers to a structurein which a first light-emitting unit 103 b and a second light-emittingunit 103 c are stacked with an intermediate layer 109 that is a chargegeneration layer positioned therebetween. Supposing a first electrode102 is an anode and the second electrode 104 is a cathode, eachlight-emitting unit typically has a structure where a hole-injectionlayer 114, a hole-transport layer 115, a light-emitting layer 116, anelectron-transport layer 117, an electron-injection layer 118, and thelike are stacked in this order from the first electrode 102 (here, ananode) side. With such a structure, a light-emitting material iscontained in the light-emitting layer 116. In the case where the firstelectrode 102 is the cathode and the second electrode 104 is the anode,the above-described order of stack in the EL layer is reversed. Notethat the EL layer 103 is shared by the first to third light-emittingelements.

One of the first light-emitting unit 103 b and the second light-emittingunit 103 c emits blue fluorescence, and the other emits greenphosphorescence. Light in which blue fluorescence and greenphosphorescence are synthesized is obtained from the EL layer 103. Thelight-emitting layer included in each of the light-emitting unitscontains a first organic compound as a host material, in addition to thelight-emitting material. Furthermore, the light-emitting layer alsocontains a second organic compound and it is preferable that the firstorganic compound and the second organic compound form an exciplex andenergy transfer occur from the exciplex to the light-emitting material.In addition, the emission spectrum of the exciplex and the absorptionband of the light-emitting material on the longest wavelength sidepreferably overlap with each other, which enables energy transfer withfavorable efficiency.

Light emitted from the first light-emitting element is extracted outsidethe light-emitting device through the color filter 107B. Light emittedfrom the second light-emitting element is extracted outside thelight-emitting device through the color filter 107G. Light emitted fromthe third light-emitting element enters the color conversion layer 106R,and the color conversion layer 106R is excited by the entering light andemits red light.

Here, the external quantum efficiency of each pixel (a light-emittingelement with components such as a color filter, a color conversionlayer, and a substrate, which affect the extraction efficiency isreferred to as a pixel, in this specification) in the light-emittingdevice having the above structure and the external quantum efficiency ofeach pixel in a light-emitting device having a structure different fromthe above will be considered. Note that the carrier balance, excitongeneration probability, and the like in light-emitting elements used inthe light-emitting devices are assumed to be similar.

First, the external quantum efficiency of each pixel in thelight-emitting device having a structure different from the above willbe calculated. In order to efficiently obtain red, green, and bluecolors with a light-emitting device using a tandem element, in general,the use of light-emitting materials having respective light emissionwavelengths is effective. In view of the practicality and efficiency, ablue fluorescent material, a red phosphorescent material, and a greenphosphorescent material are often used. A double tandem structure havingtwo light-emitting units, which is the same as FIG. 5A, is employed. Thelight-emitting layer of one of the light-emitting units is a fluorescentlayer using a blue fluorescent material, and the light-emitting layer ofthe other light-emitting unit is a phosphorescent layer using a redphosphorescent material and a green phosphorescent material.

In the light-emitting element having such a structure, the internalquantum efficiency of the fluorescent layer and that of thephosphorescent layer are assumed to be 25% and 100%, respectively. Then,the external quantum efficiency of a blue pixel is 25×χ_(CF) % (notethat χ_(CF) is the light extraction efficiency with a color filter used,and χ_(CF) is assumed to be the maximum value of the transmittance ofthe used color filter multiplied by χ_(A); and χ_(A) is the lightextraction efficiency from which the transmittance of a color filter orthe PL quantum efficiency of a color conversion layer is removed, andassumed to be common to all the pixels in the light-emitting device).The external quantum efficiency of a green pixel and that of a red pixelare each 50×χ_(CF) % (it is because excitons are divided between greenand red; for simplicity, excitons are assumed to be divided half andhalf).

Next, for the light-emitting device having the structure shown in FIG.1A, the external quantum efficiency of a blue pixel is 25×χ_(CF) %, theexternal quantum efficiency of a green pixel is 100×χ_(CF) % (thephosphorescent layer is a single layer of green; in the case where acolor filter is not provided, it is 100×χ_(A) %), and the externalquantum efficiency of a red pixel is 125×χ_(CC) (note that χ_(CC) is thelight extraction efficiency with a color conversion layer used, andχ_(CC) is assumed to be the PL quantum yield of the used colorconversion layer multiplied by χ_(A); and 125×χ_(CC) % is obtainedbecause green phosphorescence with the internal quantum efficiency of100% and blue fluorescence with the internal quantum efficiency of 25%are color-converted).

Here, the external quantum efficiency of the green pixel with thestructure of this embodiment is 100×χ_(CF) %, whereas that with theconventional structure is 50×χ_(CF) %, which means that the green pixelwith the structure of this embodiment is expected to double the externalquantum efficiency. Furthermore, the external quantum efficiency of thered pixel with the structure of this embodiment is 125×χ_(CC) %, whereasthat with the conventional structure is 50×χ_(CF) %, which means thatthe external quantum efficiency of the red pixel with the structure ofthis embodiment is expected to be 2.5 times that with the conventionalstructure, in the case where the transmittance of the color filter andthe PL quantum yield of the color conversion layer are the same.Accordingly, as long as the PL quantum yield of the color conversionlayer is greater than or equal to 40% of the transmittance of the colorfilter, a red pixel with the external quantum efficiency higher thanthat of the conventional red pixel can be obtained, and powerconsumption of the light-emitting device can be reduced. Note that thecolor filter 107G that transmits green light may be replaced by a colorconversion layer 106G. In that case, the external quantum efficiency ofthe green pixel is 125×χ_(CC) % as that of the red pixel is, and as longas the PL quantum yield χ_(CC) of the color conversion layer is greaterthan or equal to 40% of the transmittance χ_(CF) of the color filter,the green pixel with higher external quantum efficiency than that of theconventional green pixel can be obtained and power consumption of thelight-emitting device can be reduced.

As shown in FIG. 2A, a fourth light-emitting element that constitutes ayellow pixel may be added to the structure shown in FIG. 1A. The fourthlight-emitting element includes the EL layer including the firstlight-emitting unit 103 b and the second light-emitting unit 103 cbetween a first electrode 102Y and the second electrode 104. Lightemitted from the fourth light-emitting element enters a color conversionlayer 106Y, and the color conversion layer 106Y emits yellow light. Theexternal quantum efficiency of the yellow pixel is 125×χ_(CC) % becausethe yellow light is obtained by color-converting blue fluorescence withthe internal quantum efficiency of 25% and green phosphorescence withthe internal quantum efficiency of 100%.

The light-emitting device having such a structure can express an imagewith four colors, i.e., red, green, blue, and yellow, and is excellentin color reproducibility. In addition, since yellow light has a highluminosity factor, power consumption can be reduced.

<Conversion from Single Element Utilizing Blue Fluorescence and GreenPhosphorescence>

FIG. 1B shows a light-emitting device of one embodiment of the presentinvention using a single element utilizing blue fluorescence and greenphosphorescence. As with the light-emitting device shown in FIG. 1A, thelight-emitting device includes at least a first light-emitting element,a second light-emitting element, and a third light-emitting element. Asubstrate 100, a sealing substrate 101, first electrodes 102B, 102G, and102R, a second electrode 104, a black matrix 105, a color conversionlayer 106R, a color filter 107G, and a color filter 107B are alsosimilar to those of the light-emitting device shown in FIG. 1A;therefore, the description is omitted here.

In FIG. 1B, an EL layer 103 d has a single structure in which twolight-emitting layers (a first light-emitting layer 116 d-1 and a secondlight-emitting layer 116 d-2) are adjacent to each other in onelight-emitting unit, a typical example of which is shown in FIG. 5B. Thefirst light-emitting layer 116 d-1 and the second light-emitting layer116 d-2 may be formed in contact with each other, or a separation layerwith a thickness of less than or equal to 20 nm may be providedtherebetween. The thickness of the separation layer is preferablygreater than or equal to 1 nm and less than or equal to 10 nm. Note thatthe EL layer 103 d is shared by the first to third light-emittingelements.

In this structure, one of the first light-emitting layer 116 d-1 and thesecond light-emitting layer 116 d-2 in FIG. 5B emits blue fluorescence,and the other emits green phosphorescence. Light in which bluefluorescence and green phosphorescence are synthesized is obtained fromthe EL layer 103 d. The first light-emitting layer 116 d-1 and thesecond light-emitting layer 116 d-2 each contain a first organiccompound as a host material, in addition to a light-emitting material.Furthermore, the first light-emitting layer 116 d-1 and the secondlight-emitting layer 116 d-2 each contain a second organic compound aswell, and it is preferable that the first organic compound and thesecond organic compound form an exciplex and energy transfer occur fromthe exciplex to the light-emitting materials. In addition, the emissionspectrum of the exciplex and the absorption band of the light-emittingmaterial on the longest wavelength side preferably overlap with eachother, which enables energy transfer with favorable efficiency.

Light emitted from the first light-emitting element is extracted outsidethe light-emitting device through the blue color filter 107B. Lightemitted from the second light-emitting element is extracted outside thelight-emitting device through the green color filter 107G. Light emittedfrom the third light-emitting element enters the color conversion layer106R, and the color conversion layer 106R is excited by the enteringlight and emits red light.

Here, the external quantum efficiency of each pixel in thelight-emitting device having the above structure and the externalquantum efficiency of each pixel in a light-emitting device having astructure different from the above will be considered. Note that thecarrier balance, exciton generation probability, and the like inlight-emitting elements used in the light-emitting devices are assumedto be similar.

First, the external quantum efficiency of each pixel in thelight-emitting device having a structure different from the above willbe calculated. In order to obtain red, green, and blue colors with thelight-emitting device using light-emitting elements having asingle-structure EL layer in which two light-emitting layers areadjacent to each other in one light-emitting unit, without the use of acolor conversion layer, light-emitting materials that emit light withintensity at the wavelengths corresponding to the colors are required.If a blue fluorescent material, a red phosphorescent material, and agreen phosphorescent material are used in view of the practicality andefficiency; it is preferable that the blue fluorescent material be usedfor one of the first light-emitting layer 116 d-1 and the secondlight-emitting layer 116 d-2, and that the red phosphorescent materialand the green phosphorescent material be used for the other. Assumingthat the internal quantum efficiency of a fluorescent layer in thelight-emitting element is 25%, the internal quantum efficiency of aphosphorescent layer in the light-emitting element is 100%, and excitonsare divided equally between blue, green, and red; the external quantumefficiency of a blue pixel is 8.3×χ_(CF) %, and the external quantumefficiency of a green pixel and that of a red pixel are each 33.3×χ_(CF)%.

Next, the light-emitting device having the structure shown in FIG. 1Bwill be considered. In addition to the assumption similar to the above,it is assumed that excitons are divided equally between blue and green;thus, the external quantum efficiency of the blue pixel is 12.5×χ_(CF)%, the external quantum efficiency of the green pixel is 50×χ_(CF) %,and the external quantum efficiency of the red pixel is 62.5×χ_(CC) %.In this way, the use of the structure of one embodiment of the presentinvention provides a light-emitting element with much higher efficiencythan that of the conventional element. Note that the color filter 107Gthat transmits green light can be replaced by a color conversion layer106G. In that case, the external quantum efficiency of the green pixelis 62.5×χ_(CC) % as that of the red pixel is.

Here, the external quantum efficiency of each pixel with theconventional structure and each pixel with the structure of thisembodiment will be compared. The external quantum efficiency of the bluepixel with the structure of this embodiment is 12.5×χ_(CF) % whereasthat with the conventional structure is 8.3×χ_(CF) %, which means thatthe external quantum efficiency of the blue pixel with the structure ofthis embodiment is expected to be approximately 1.5 times that with theconventional structure. The external quantum efficiency of the greenpixel with the structure of this embodiment is 50×χ_(CF) % whereas thatwith the conventional structure is 33×χ_(CF) %, which means that theexternal quantum efficiency of the green pixel with the structure ofthis embodiment is expected to be also approximately 1.5 times that withthe conventional structure. The external quantum efficiency of the redpixel with the structure of this embodiment is 62.5×χ_(CC) % whereasthat with the conventional structure is 33×χ_(CF) %, which means thatthe external quantum efficiency of the red pixel with the structure ofthis embodiment is expected to be approximately 1.88 times that with theconventional structure in the case where the transmittance of the colorfilter and the PL quantum yield of the color conversion layer are thesame. Accordingly, as long as the PL quantum yield of the colorconversion layer is greater than or equal to 53.3% of the transmittanceof the color filter, a red pixel with the external quantum efficiencyhigher than that of the conventional red pixel can be obtained, andpower consumption of the light-emitting device can be reduced.

As shown in FIG. 2B, a fourth light-emitting element that constitutes ayellow pixel may be added to the structure shown in FIG. 1B. The fourthlight-emitting element includes the EL layer with a single structure inwhich two light-emitting layers (the first light-emitting layer 116 d-1and the second light-emitting layer 116 d-2) are adjacent to each other,between a first electrode 102Y and the second electrode 104. Lightemitted from the fourth light-emitting element enters a color conversionlayer 106Y, and the color conversion layer 106Y emits yellow light. Theexternal quantum efficiency of the yellow pixel is 62.5×χ_(CC) % becausethe yellow light is obtained by color-converting blue fluorescence andgreen phosphorescence.

The light-emitting device having such a structure can express an imagewith four colors, i.e., red, green, blue, and yellow, and is excellentin color reproducibility. In addition, since yellow light has a highluminosity factor, power consumption can be reduced.

<Conversion from Single Element of Blue Fluorescence and Single Elementof Green Phosphorescence (One Selective Deposition Step Using Mask) 1>

FIG. 1C shows a light-emitting device of one embodiment of the presentinvention using a single element of blue fluorescence and a singleelement of green phosphorescence. As with the light-emitting deviceshown in FIG. 1A, the light-emitting device includes at least a firstlight-emitting element, a second light-emitting element, and a thirdlight-emitting element. A substrate 100, a sealing substrate 101, firstelectrodes 102B, 102G, and 102R, a second electrode 104, a black matrix105, and a color conversion layer 106R are also similar to those of thelight-emitting device shown in FIG. 1A; therefore, the description isomitted here.

In the light-emitting device shown in FIG. 1C, the first light-emittingelement includes an EL layer with a first structure, and the secondlight-emitting element and the third light-emitting element include anEL layer with a second structure.

The EL layer with the first structure is a stack including a first ELlayer 103 e, a second EL layer 103 f, a third EL layer 103 g, and afourth EL layer 103 h. The EL layer with the second structure is a stackincluding the first EL layer 103 e, the third EL layer 103 g, and thefourth EL layer 103 h.

In the case where the first electrodes are anodes and the secondelectrode is a cathode, the first EL layer 103 e corresponds to ahole-injection layer 114 and a hole-transport layer 115 in FIG. 5B, thesecond EL layer 103 f corresponds to the first light-emitting layer 116d-1 in FIG. 5B, the third EL layer 103 g corresponds to the secondlight-emitting layer 116 d-2 in FIG. 5B, and the fourth EL layer 103 hcorresponds to an electron-transport layer 117 and an electron-injectionlayer 118 in FIG. 5B. That is, the EL layer with the first structure hasa structure similar to that of the EL layer 103 d in FIG. 5B, and the ELlayer with the second structure has a structure similar to that of an ELlayer 103 a in FIG. 5C.

Formation of the EL layer with the first structure and the EL layer withthe second structure requires only one selective deposition step thatuses a mask. That is, only one selective deposition step that uses amask leads to much higher efficiency of light emission than that of ausual light-emitting element with a single structure in which afluorescent layer and a phosphorescent layer are stacked.

The second EL layer 103 f contains an organic compound that emits bluefluorescence as a light-emitting material, and the third EL layer 103 gcontains an organic compound that emits green phosphorescence as alight-emitting material. The second EL layer 103 f and the third ELlayer 103 g each contain a first organic compound as a host material, inaddition to their respective light-emitting materials. Furthermore, thesecond EL layer 103 f and the third EL layer 103 g each contain a secondorganic compound as well, and it is preferable that the first organiccompound and the second organic compound form an exciplex and energytransfer occur from the exciplex to the light-emitting materials. Inaddition, the emission spectrum of the exciplex and the absorption bandof the light-emitting material on the longest wavelength side preferablyoverlap with each other, which enables energy transfer with favorableefficiency.

In the light-emitting device with this structure, it is preferable thatthe second EL layer 103 f and the third EL layer 103 g be each a layerin which the electron-transport property is higher than thehole-transport property. With such a structure, only blue fluorescencecan be obtained from the first light-emitting element, and only greenphosphorescence can be obtained from the second light-emitting elementand the third light-emitting element. Note that in the case where thefirst electrodes are cathodes and the second electrode is an anode, thefirst EL layer 103 e corresponds to the electron-transport layer 117 andthe electron-injection layer 118 in FIG. 5B, the fourth EL layer 103 hcorresponds to the hole-injection layer 114 and the hole-transport layer115 in FIG. 5B, and it is preferable that the second EL layer 103 f andthe third EL layer 103 g be each a layer in which the hole-transportproperty is higher than the electron-transport property.

Although the second EL layer 103 f in FIG. 1C is formed before the thirdEL layer 103 g is formed, the third EL layer 103 g may be formed beforethe second EL layer 103 f is formed. In that case, it is preferable thatthe second EL layer 103 f and the third EL layer 103 g be each a layerin which the hole-transport property is higher than theelectron-transport property. In the case where the first electrode is acathode and the second electrode is an anode, it is preferable that thesecond EL layer 103 f and the third EL layer 103 g be each a layer inwhich the electron-transport property is higher than the hole-transportproperty.

When light emitted from the third light-emitting element enters thecolor conversion layer 106R, red light can be obtained from the colorconversion layer 106R. Note that light emitted from the firstlight-emitting element and light emitted from the second light-emittingelement may be extracted outside the light-emitting device through colorfilters. Without color filters, light can be obtained with highefficiency. Emitted through color filters, light can be obtained withhigh color purity.

Here, the external quantum efficiency of each pixel in thelight-emitting device having the above structure and the externalquantum efficiency of each pixel in a light-emitting device having astructure different from the above will be considered. Note that thecarrier balance, exciton generation probability, and the like inlight-emitting elements used in the light-emitting devices are assumedto be similar.

First, the external quantum efficiency of each pixel in thelight-emitting device having a structure without a color conversionlayer, which is different from the above, will be calculated. Thestructures of the light-emitting elements in the light-emitting deviceare similar to the structures of the light-emitting elements in thelight-emitting device shown in FIG. 1C. In order to efficiently obtainred, green, and blue colors with the light-emitting device, in general,light-emitting materials that emit light having intensity at thewavelengths corresponding to the colors are required. In the case wherea blue fluorescent material, a red phosphorescent material, and a greenphosphorescent material are used in view of practicality and efficiency,the blue fluorescent material is used for the second EL layer 103 f, andthe red phosphorescent material and the green phosphorescent materialare used for the third EL layer 103 g. Light in which red light andgreen light are synthesized is obtained from the second light-emittingelement and the third light-emitting element. Therefore, light from thesecond light-emitting element is extracted outside the light-emittingdevice through a green color filter, whereby green light emission can beobtained, and light from the third light-emitting element is extractedoutside the light-emitting device through a red color filter, wherebyred light emission can be obtained.

In the light-emitting element having such a structure, the internalquantum efficiency of the fluorescent layer and that of thephosphorescent layer are assumed to be 25% and 100%, respectively. Then,the external quantum efficiency of a blue pixel is 25×χ_(A) % (when acolor filter is not used; it is 25×χ_(CF) % when a color filter isused), and the external quantum efficiency of a green pixel and that ofa red pixel are each 50×χ_(CF) %.

Next, for the light-emitting device having the structure shown in FIG.1C, the external quantum efficiency of a blue pixel is 25×χ_(A) % (whena color filter is not used; it is 25×χ_(CF) % when a color filter isused), the external quantum efficiency of a green pixel is 100×χ_(A) %(when a color filter is not used; it is 100×χ_(CF) % when a color filteris used), and the external quantum efficiency of a red pixel is100×χ_(CC) %. In this way, the use of the structure of one embodiment ofthe present invention can provide a light-emitting device with very highlight emission efficiency.

Here, the external quantum efficiency of the green pixel with thestructure of this embodiment is 100×χ_(A) %, whereas that with theconventional structure is 50×χ_(CF) %, which means that the externalquantum efficiency of the green pixel with the structure of thisembodiment is expected to be twice or more that with the conventionalstructure. Furthermore, the external quantum efficiency of the red pixelwith the structure of this embodiment is 100×χ_(CC) %, whereas that withthe conventional structure is 50×χ_(CF) %, which means that the externalquantum efficiency of the red pixel with the structure of thisembodiment is expected to be twice that with the conventional structure,in the case where the transmittance of the color filter and the PLquantum yield of the color conversion layer are the same. Accordingly,as long as the PL quantum yield of the color conversion layer is greaterthan or equal to 50% of the transmittance of the color filter, a redpixel with the external quantum efficiency higher than that of theconventional red pixel can be obtained, and power consumption of thelight-emitting device can be reduced.

As shown in FIG. 2C, a fourth light-emitting element that constitutes ayellow pixel may be added to the structure shown in FIG. 1C. The fourthlight-emitting element includes the EL layer with the second structurebetween a first electrode 102Y and the second electrode 104. Lightemitted from the fourth light-emitting element enters a color conversionlayer 106Y, and the color conversion layer 106Y emits yellow light. Theexternal quantum efficiency of the yellow pixel is 100×χ_(CC) % becausethe yellow light is obtained by color-converting green phosphorescence.

The light-emitting device having such a structure can express an imagewith four colors, i.e., red, green, blue, and yellow, and is excellentin color reproducibility. In addition, since yellow light has a highluminosity factor, power consumption can be reduced.

<Conversion from Single Element of Blue Fluorescence and Single Elementof Green Phosphorescence (One Selective Deposition Step Using Mask) 2>

FIG. 1D shows a light-emitting device of one embodiment of the presentinvention using a single element of blue fluorescence and a singleelement of green phosphorescence. As with the light-emitting deviceshown in FIG. 1A, the light-emitting device includes at least a firstlight-emitting element, a second light-emitting element, and a thirdlight-emitting element. A substrate 100, a sealing substrate 101, firstelectrodes 102B, 102G, and 102R, a second electrode 104, a black matrix105, and a color conversion layer 106R are also similar to those of thelight-emitting device shown in FIG. 1A; therefore, the description isomitted here.

In the light-emitting device shown in FIG. 1D, the first light-emittingelement includes an EL layer with a third structure, and the secondlight-emitting element and the third light-emitting element include anEL layer with a fourth structure.

The EL layer with the third structure is a stack including a first ELlayer 103 i, a second EL layer 103 j, and a fourth EL layer 103 m. TheEL layer with the fourth structure is a stack including the first ELlayer 103 i, the second EL layer 103 j, a third EL layer 103 k, and thefourth EL layer 103 m.

In the case where the first electrodes are anodes and the secondelectrode is a cathode, the first EL layer 103 i corresponds to thehole-injection layer 114 and the hole-transport layer 115 in FIG. 5B,the second EL layer 103 j corresponds to the first light-emitting layer116 d-1 in FIG. 5B, the third EL layer 103 k corresponds to the secondlight-emitting layer 116 d-2 in FIG. 5B, and the fourth EL layer 103 mcorresponds to the electron-transport layer 117 and theelectron-injection layer 118 in FIG. 5B. That is, the EL layer with thefourth structure has a structure similar to that of the EL layer 103 din FIG. 5B, and the EL layer with the third structure has a structuresimilar to that of the EL layer 103 a in FIG. 5C.

Formation of the EL layer with the third structure and the EL layer withthe fourth structure requires only one selective deposition step thatuses a mask. That is, only one selective deposition step that uses amask leads to much higher efficiency of light emission than that of ausual light-emitting element with a single structure in which afluorescent layer and a phosphorescent layer are stacked.

The second EL layer 103 j contains an organic compound that emits bluefluorescence as a light-emitting material, and the third EL layer 103 kcontains an organic compound that emits green phosphorescence as alight-emitting material. The second EL layer 103 j and the third ELlayer 103 k each contain a first organic compound as a host material, inaddition to the light-emitting material. Furthermore, the second ELlayer 103 j and the third EL layer 103 k each contain a second organiccompound as well, and it is preferable that the first organic compoundand the second organic compound form an exciplex and energy transferoccur from the exciplex to the light-emitting material. In addition, theemission spectrum of the exciplex and the absorption band of thelight-emitting material on the longest wavelength side preferablyoverlap with each other, which enables energy transfer with favorableefficiency.

In the light-emitting device with this structure, it is preferable thatthe second EL layer 103 j and the third EL layer 103 k be each a layerin which the hole-transport property is higher than theelectron-transport property. With such a structure, only bluefluorescence can be obtained from the first light-emitting element, andonly green phosphorescence can be obtained from the secondlight-emitting element and the third light-emitting element. Note thatin the case where the first electrodes are cathodes and the secondelectrode is an anode, the first EL layer 103 i corresponds to theelectron-transport layer 117 and the electron-injection layer 118 inFIG. 5B, the fourth EL layer 103 m corresponds to the hole-injectionlayer 114 and the hole-transport layer 115 in FIG. 5B, and it ispreferable that the second EL layer 103 j and the third EL layer 103 kbe each a layer in which the electron-transport property is higher thanthe hole-transport property.

Although the second EL layer 103 j in FIG. 1D is formed before the thirdEL layer 103 k is formed, the third EL layer 103 k may be formed beforethe second EL layer 103 j is formed. In that case, it is preferable thatthe second EL layer 103 j and the third EL layer 103 k be each a layerin which the hole-transport property is higher than theelectron-transport property. In the case where the first electrode is acathode and the second electrode is an anode, it is preferable that thesecond EL layer 103 j and the third EL layer 103 k be each a layer inwhich the electron-transport property is higher than the hole-transportproperty.

When light emitted from the third light-emitting element enters thecolor conversion layer 106R, red light can be obtained from the colorconversion layer 106R. Note that light emitted from the firstlight-emitting element and light emitted from the second light-emittingelement may be extracted outside the light-emitting device through colorfilters. Without color filters, light can be obtained with highefficiency. Emitted through color filters, light can be obtained withhigh color purity.

Here, the external quantum efficiency of each pixel in thelight-emitting device having the above structure and the externalquantum efficiency of each pixel in a light-emitting device having astructure different from the above will be considered. Note that thecarrier balance, exciton generation probability, and the like inlight-emitting elements used in the light-emitting devices are assumedto be similar.

First, the external quantum efficiency of each pixel in thelight-emitting device having a structure without a color conversionlayer, which is different from the above, will be calculated. Thestructures of the light-emitting elements in the light-emitting deviceare similar to the structures of the light-emitting elements in thelight-emitting device shown in FIG. 1D. In order to efficiently obtainred, green, and blue colors with the light-emitting device, in general,light-emitting materials that emit light having intensity at thewavelengths corresponding to the colors are required. In the case wherea blue fluorescent material, a red phosphorescent material, and a greenphosphorescent material are used in view of practicality and efficiency,it is preferable that the blue fluorescent material be used for thesecond EL layer 103 j, and the red phosphorescent material and the greenphosphorescent material be used for the third EL layer 103 k. Light inwhich red light and green light are synthesized is obtained from thesecond light-emitting element and the third light-emitting element.Therefore, light from the second light-emitting element is extractedoutside the light-emitting device through a green color filter, wherebygreen light emission can be obtained, and light from the thirdlight-emitting element is extracted outside the light-emitting devicethrough a red color filter, whereby red light emission can be obtained.

In the light-emitting element having such a structure, the internalquantum efficiency of the fluorescent layer and that of thephosphorescent layer are assumed to be 25% and 100%, respectively. Then,the external quantum efficiency of a blue pixel is 25×χ_(A) % (when acolor filter is not used; it is 25×χ_(CF) % when a color filter isused), and the external quantum efficiency of a green pixel and that ofa red pixel are each 50×χ_(CF) %.

Next, for the light-emitting device having the structure shown in FIG.1D, the external quantum efficiency of a blue pixel is 25×χ_(A) % (whena color filter is not used; it is 25×χ_(CF) % when a color filter isused), the external quantum efficiency of a green pixel is 100×χ_(A) %(when a color filter is not used; it is 100×χ_(CF) % when a color filteris used), and the external quantum efficiency of a red pixel is100×χ_(CC) %. In this way, the use of the structure of one embodiment ofthe present invention can provide a light-emitting device with very highlight emission efficiency.

Here, the external quantum efficiency of the green pixel with thestructure of this embodiment is 100×χ_(A) %, whereas that with theconventional structure is 50×χ_(CF) %, which means that the externalquantum efficiency of the green pixel with the structure of thisembodiment is expected to be twice or more that with the conventionalstructure. Furthermore, the external quantum efficiency of the red pixelwith the structure of this embodiment is 100×χ_(CC) %, whereas that withthe conventional structure is 50×χ_(CF) %, which means that the externalquantum efficiency of the red pixel with the structure of thisembodiment is expected to be twice that with the conventional structure,in the case where the transmittance of the color filter and the PLquantum yield of the color conversion layer are the same. Accordingly,as long as the PL quantum yield of the color conversion layer is greaterthan or equal to 50% of the transmittance of the color filter, a redpixel with the external quantum efficiency higher than that of theconventional red pixel can be obtained, and power consumption of thelight-emitting device can be reduced.

As shown in FIG. 2D, a fourth light-emitting element that constitutes ayellow pixel may be added to the structure shown in FIG. 1D. The fourthlight-emitting element includes the EL layer with the fourth structurebetween a first electrode 102Y and the second electrode 104. Lightemitted from the fourth light-emitting element enters a color conversionlayer 106Y, and the color conversion layer 106Y emits yellow light. Theexternal quantum efficiency of the yellow pixel is 100×χ_(CC) % becausethe yellow light is obtained by color-converting green phosphorescence.

The light-emitting device having such a structure can express an imagewith four colors, i.e., red, green, blue, and yellow, and is excellentin color reproducibility. In addition, since yellow light has a highluminosity factor, power consumption can be reduced.

<Conversion from Tandem Element of Blue Fluorescence and YellowPhosphorescence>

FIG. 3A shows a light-emitting device of one embodiment of the presentinvention using a tandem element of blue fluorescence and yellowphosphorescence. The light-emitting device includes at least a firstlight-emitting element, a second light-emitting element, and a thirdlight-emitting element provided over a substrate 100. The first to thirdlight-emitting elements share an EL layer 103 and a second electrode104, and each have a different first electrode. The first light-emittingelement, the second light-emitting element, and the third light-emittingelement have a first electrode 102B, a first electrode 102G, and a firstelectrode 102R, respectively. A sealing substrate 101 is provided with ablack matrix 105, a color filter 107B, a color conversion layer 106G,and a color conversion layer 106R. The color filter 107B transmits bluelight. The color conversion layer 106G contains a color conversionsubstance that emits green light, and the color conversion layer 106Rcontains a color conversion substance that emits red light.

In FIG. 3A, the EL layer 103 has a tandem structure, a typical exampleof which is shown in FIG. 5A. The tandem structure refers to a structurein which a first light-emitting unit 103 b and a second light-emittingunit 103 c are stacked with an intermediate layer 109 that is a chargegeneration layer positioned therebetween. Supposing a first electrode102 is an anode and the second electrode 104 is a cathode, eachlight-emitting unit typically has a structure where a hole-injectionlayer 114, a hole-transport layer 115, a light-emitting layer 116, anelectron-transport layer 117, an electron-injection layer 118, and thelike are stacked in this order from the first electrode 102 (here, ananode) side. With such a structure, a light-emitting material iscontained in the light-emitting layer 116. In the case where the firstelectrode 102 is the cathode and the second electrode 104 is the anode,the above-described order of stack in the EL layer is reversed. Notethat the EL layer 103 is shared by the first to third light-emittingelements.

One of the first light-emitting unit 103 b and the second light-emittingunit 103 c emits blue fluorescence, and the other emits yellowphosphorescence. Light in which blue fluorescence and yellowphosphorescence are synthesized is obtained from the EL layer 103. Thelight-emitting layer included in each of the light-emitting unitcontains a first organic compound as a host material, in addition to thelight-emitting material. Furthermore, the light-emitting layer alsocontains a second organic compound, and it is preferable that the firstorganic compound and the second organic compound form an exciplex andenergy transfer occur from the exciplex to the light-emitting material.In addition, the emission spectrum of the exciplex and the absorptionband of the light-emitting material on the longest wavelength sidepreferably overlap with each other, which enables energy transfer withfavorable efficiency.

Light emitted from the first light-emitting element is extracted outsidethe light-emitting device through the color filter 107B. Light emittedfrom the second light-emitting element enters the color conversion layer106G, and the color conversion layer 106G is excited by the enteringlight and emits green light. Light emitted from the third light-emittingelement enters the color conversion layer 106R, and the color conversionlayer 106R emits red light.

Note that in this light-emitting device, light in which bluefluorescence and yellow phosphorescence are synthesized is emitted fromthe EL layer 103; however, the color conversion layer 106G cannot absorbyellow light. Thus, it is preferable that yellow light that enters thecolor conversion layer 106G be removed with the use of a resonantstructure or a color filter. When the resonant structure is formed, itis formed such that blue light is amplified. The resonant structures canbe provided by forming transparent conductive films (i.e., a transparentconductive film 102Bt, a transparent conductive film 102Gt, and atransparent conductive film 102Rt) with desired thicknesses over thefirst electrodes, as shown in FIG. 3A. Note that the resonant structuresneed not be formed in the first light-emitting element and the thirdlight-emitting element for the purpose of removing light that cannot beabsorbed. In the case where the resonant structures are formed for theother purpose, the transparent conductive film 102Bt may be formed suchthat blue light is amplified in the first light-emitting element, andthe transparent conductive film 102Rt may be formed such that yellowlight is amplified in the third light-emitting element.

Here, the external quantum efficiency of each pixel in thelight-emitting device having the above structure and the externalquantum efficiency of each pixel in a light-emitting device having astructure different from the above will be considered. Note that thecarrier balance, exciton generation probability, and the like inlight-emitting elements used in the light-emitting devices are assumedto be similar.

First, the external quantum efficiency of each color pixel in thelight-emitting device having a structure different from the above willbe calculated. In order to efficiently obtain red, green, and bluecolors with a light-emitting device using a tandem element, in general,the use of light-emitting materials having respective light emissionwavelengths is effective. In view of the practicality and efficiency, ablue fluorescent material, a red phosphorescent material, and a greenphosphorescent material are often used. A double tandem structure, whichis the same as FIG. 5A, is employed. The light-emitting layer of one ofthe light-emitting units is a fluorescent layer using a blue fluorescentmaterial, and the light-emitting layer of the other light-emitting unitis a phosphorescent layer using a red phosphorescent material and agreen phosphorescent material.

In the light-emitting element having such a structure, the internalquantum efficiency of the fluorescent layer and that of thephosphorescent layer are assumed to be 25% and 100%, respectively. Then,the external quantum efficiency of a blue pixel is 25×χ_(CF) %, and theexternal quantum efficiency of a green pixel and that of a red pixel areeach 50×χ_(CF) % (It is because excitons are divided between the redphosphorescent material and the green phosphorescent material in thephosphorescent layer. For simplicity, excitons are assumed to be dividedhalf and half).

Next, the light-emitting device having the above structure (thestructure shown in FIG. 3A) will be considered. The external quantumefficiency of the blue pixel, that of the green pixel, and that of thered pixel are 25×χ_(CF) %, 25×χ_(CC) %, and 125×χ_(CC) % (in the casewhere a resonant structure is not formed; it is 100×χ_(CC) % in the casewhere a resonant structure is formed, because blue light attenuates),respectively. In this way, the use of the light-emitting elements of oneembodiment of the present invention can greatly increase the efficiencyof red light emission.

Here, the external quantum efficiency of the red pixel with thestructure of this embodiment is 125×χ_(CC) %, whereas that with theconventional structure is 50×χ_(CF) %, which means that the externalquantum efficiency of the red pixel with the structure of thisembodiment is expected to be 2.5 times that with the conventionalstructure, in the case where the transmittance of the color filter andthe PL quantum yield of the color conversion layer are the same.Accordingly, as long as the PL quantum yield of the color conversionlayer is greater than or equal to 40% of the transmittance of the colorfilter, a red pixel with the external quantum efficiency higher thanthat of the conventional red pixel can be obtained.

As shown in FIG. 4A, a fourth light-emitting element as a yellow pixelmay be added to the structure shown in FIG. 3A. The fourthlight-emitting element includes the EL layer including the firstlight-emitting unit 103 b and the second light-emitting unit 103 cbetween a first electrode 102Y and the second electrode 104. A resonantstructure corresponding to yellow light emission may be provided, inwhich case a transparent conductive film 102Yt may be formed. Sincelight emitted from the fourth light-emitting element is extractedoutside the light-emitting device through a color filter 107Y, theexternal quantum efficiency of the yellow pixel is 100×χ_(CF) %. Thecolor filter 107Y may be replaced by a yellow color conversion layer106Y, in which case the external quantum efficiency of the yellow pixelis 125×χ_(CC) %.

The light-emitting device having such a structure can express an imagewith four colors, i.e., red, green, blue, and yellow, and is excellentin color reproducibility. In addition, since yellow light has a highluminosity factor, power consumption can be reduced.

Note that in the case where the structure shown in FIG. 4A is employed,white light can be expressed only with red, blue, and yellow light, andthus the efficiency of green light hardly affects the power consumption.Accordingly, in view of the efficiency of the yellow pixel being 100%, alight-emitting device with higher efficiency than that of a conventionallight-emitting device can be obtained as long as the PL quantum yield ofthe color conversion layer 106R, which is a first color conversion layerprovided in the red pixel, is higher than 40%. In the case where theresonant structure is formed, the light-emitting device can have higherefficiency than that of a conventional light-emitting device as long asthe PL quantum yield of the color conversion layer 106R is higher than50%.

<Conversion from Single Element of Blue Fluorescence and YellowPhosphorescence>

FIG. 3B shows a light-emitting device of one embodiment of the presentinvention using a single element utilizing blue fluorescence and yellowphosphorescence. As with the light-emitting device shown in FIG. 3A, thelight-emitting device includes at least a first light-emitting element,a second light-emitting element, and a third light-emitting element. Asubstrate 100, a sealing substrate 101, first electrodes 102B, 102G, and102R, a second electrode 104, a black matrix 105, a color conversionlayer 106R, a color conversion layer 106G, and a color filter 107B arealso similar to those of the light-emitting device shown in FIG. 3A;therefore, the description is omitted here.

In FIG. 3B, an EL layer 103 d has a single structure, a typical exampleof which is shown in FIG. 5B. The first light-emitting layer 116 d-1 andthe second light-emitting layer 116 d-2 may be formed in contact witheach other, or a separation layer with a thickness of less than or equalto 20 nm may be provided therebetween. The thickness of the separationlayer is preferably greater than or equal to 1 nm and less than or equalto 10 nm. Note that the EL layer 103 d is shared by the first to thirdlight-emitting elements.

In this structure, one of the first light-emitting layer 116 d-1 and thesecond light-emitting layer 116 d-2 in FIG. 5B emits blue fluorescence,and the other emits yellow phosphorescence. Light in which bluefluorescence and yellow phosphorescence are synthesized is obtained fromthe EL layer 103 d. The first light-emitting layer 116 d-1 and thesecond light-emitting layer 116 d-2 each contain a first organiccompound as a host material, in addition to a light-emitting material.Furthermore, the first light-emitting layer 116 d-1 and the secondlight-emitting layer 116 d-2 each contain a second organic compound aswell, and it is preferable that the first organic compound and thesecond organic compound form an exciplex and energy transfer occur fromthe exciplex to the light-emitting materials. In addition, the emissionspectrum of the exciplex and the absorption band of the light-emittingmaterial on the longest wavelength side preferably overlap with eachother, which enables energy transfer with favorable efficiency.

Light emitted from the first light-emitting element is extracted outsidethe light-emitting device through the blue color filter 107B. Lightemitted from the second light-emitting element enters the colorconversion layer 106G, and the color conversion layer 106G is excited bythe entering light and emits green light. Similarly, light emitted fromthe third light-emitting element enters the color conversion layer 106R,and the color conversion layer 106R emits red light.

Note that in this light-emitting device, light in which bluefluorescence and yellow phosphorescence are synthesized is emitted fromthe EL layer 103, As with FIG. 3A; however, the color conversion layer106G cannot absorb yellow light. Thus, it is preferable that yellowlight that enters the color conversion layer 106G be removed with theuse of a resonant structure or a color filter. When the resonantstructure is formed, it is formed such that blue light is amplified. Theresonant structures can be provided by forming transparent conductivefilms (a transparent conductive film 102Bt, a transparent conductivefilm 102Gt, and a transparent conductive film 102Rt) with desiredthicknesses over the first electrodes, as shown in FIG. 3B. Note thatthe resonant structures need not be formed in the first light-emittingelement and the third light-emitting element for the purpose of removinglight that cannot be absorbed. In the case where the resonant structuresare formed for the other purpose, the transparent conductive film 102Btmay be formed such that blue light is amplified in the firstlight-emitting element, and the transparent conductive film 102Rt may beformed such that yellow light is amplified in the third light-emittingelement.

Here, the external quantum efficiency of each pixel in thelight-emitting device having the above structure and the externalquantum efficiency of each pixel in a light-emitting device having astructure different from the above will be considered. Note that thecarrier balance, exciton generation probability, and the like inlight-emitting elements used in the light-emitting devices are assumedto be similar.

First, the external quantum efficiency of each pixel in thelight-emitting device having a structure different from the above willbe calculated. The light-emitting elements have a single-structure ELlayer in which two light-emitting layers are adjacent to each other inone light-emitting unit as shown in FIG. 5B. In order to obtain red,green, and blue colors with the light-emitting elements having such astructure, without the use of a color conversion layer, the use oflight-emitting materials having respective light emission wavelengths iseffective. In view of practicality and efficiency, a blue fluorescentmaterial, a red phosphorescent material, and a green phosphorescentmaterial are often used. When one of the first light-emitting layer 116d-1 and the second light-emitting layer 116 d-2 is a fluorescent layerand the other is a phosphorescent layer, the blue fluorescent materialis contained in one of the light-emitting layers, and the redphosphorescent material and the green phosphorescent material arecontained in the other light-emitting layer. Assuming that the internalquantum efficiency of the fluorescent layer is 25% and that of thephosphorescent layer is 100%, and that excitons are divided equallybetween blue, green, and red (i.e., 1:1:1); the external quantumefficiency of a blue pixel is 8.3×χ_(CF) %, and that of a green pixeland that of a red pixel are each 33×χ_(CF) %.

Next, the light-emitting device having a structure shown in FIG. 3B willbe considered. In addition to the assumption similar to the above, it isassumed that excitons are divided between blue and yellow half and half(1:1) and that the PL quantum yield of color conversion layers is 100%;thus, the external quantum efficiency of a blue pixel, that of a greenpixel, and that of a red pixel are 12.5×χ_(CF) %, 12.5×χ_(CC) %, and62.5×χ_(CC) % (in the case where a resonant structure is not used; it is50×χ_(CC) % in the case where a resonant structure is used, because bluelight attenuates), respectively. In this way, the use of thelight-emitting elements of one embodiment of the present invention cangreatly increase the external quantum efficiency of the red pixel.

Here, the external quantum efficiency of the blue pixel with thestructure of this embodiment is 12.5×χ_(CF) %, whereas that with theconventional structure is 8.3×χ_(CF) %, which means that the externalquantum efficiency of the blue pixel with the structure of thisembodiment is expected to be approximately 1.5 times that with theconventional structure. Furthermore, the external quantum efficiency ofthe red pixel with the structure of this embodiment is 62.5×χ_(CC) %,whereas that with the conventional structure is 33×χ_(CF) %, which meansthat the external quantum efficiency of the red pixel with the structureof this embodiment is expected to be approximately 1.88 times that withthe conventional structure, in the case where the transmittance of thecolor filter and the PL quantum yield of the color conversion layer arethe same. Accordingly, as long as the PL quantum yield of the colorconversion layer in the red pixel is greater than or equal to 53.3% ofthe transmittance of the color filter, a red pixel with the externalquantum efficiency higher than that of the conventional red pixel can beobtained

As shown in FIG. 4B, a fourth light-emitting element that constitutes ayellow pixel may be added to the structure shown in FIG. 3B. The fourthlight-emitting element includes the EL layer 103 d between a firstelectrode 102Y and the second electrode 104. Light emitted from thefourth light-emitting element is extracted outside the light-emittingdevice through a color filter 107Y, so that the external quantumefficiency of the yellow pixel is 50×χ_(CF) %. When a resonant structureis formed, it is formed such that yellow light is amplified. Theresonant structure can be provided by forming a transparent conductivefilm 102Yt with a desired thickness over the first electrode, as shownin FIG. 4B. Furthermore, the color filter 107Y may be replaced by ayellow color conversion layer 106Y, in which case the external quantumefficiency of the yellow pixel is 62.5×χ_(CC) %.

The light-emitting device having such a structure can express an imagewith four colors, i.e., red, green, blue, and yellow, and is excellentin color reproducibility. In addition, since yellow light has a highluminosity factor, power consumption can be reduced.

Note that in the case where the structure shown in FIG. 4B is employed,white light can be expressed only with red, blue, and yellow light, andthus the efficiency of green light hardly affects the power consumption.Accordingly, in view of the external quantum efficiency of the yellowpixel being 50×χ_(CF) %, a light-emitting device with higher efficiencythan that of a conventional light-emitting device can be obtained aslong as the PL quantum yield of the color conversion layer 106R, whichis a first color conversion layer provided in the red pixel, is greaterthan 53.3% of the transmittance (%) of the red color filter. In the casewhere the resonant structure is formed, the light-emitting device canhave a higher efficiency than that of a conventional light-emittingdevice as long as the PL quantum yield of the color conversion layer106R is greater than 66% of the transmittance (%) of the red colorfilter.

<Conversion from Single Element of Blue Fluorescence and Single Elementof Yellow Phosphorescence (One Selective Deposition Step Using Mask) 1>

FIG. 3C shows a light-emitting device of one embodiment of the presentinvention using a single element of blue fluorescence and a singleelement of yellow phosphorescence. As with the light-emitting deviceshown in FIG. 3A, the light-emitting device includes at least a firstlight-emitting element, a second light-emitting element, and a thirdlight-emitting element. A substrate 100, a sealing substrate 101, firstelectrodes 102B, 102G, and 102R, a second electrode 104, a black matrix105, and color conversion layers 106G and 106R are also similar to thoseof the light-emitting device shown in FIG. 3A; therefore, thedescription is omitted here.

In the light-emitting device shown in FIG. 3C, the first light-emittingelement and the second light-emitting element include an EL layer with afifth structure, and the third light-emitting element includes an ELlayer with a sixth structure.

The EL layer with the fifth structure is a stack including a first ELlayer 103 e, a second EL layer 103 f, a third EL layer 103 g, and afourth EL layer 103 h. The EL layer with the sixth structure is a stackincluding the first EL layer 103 e, the third EL layer 103 g, and thefourth EL layer 103 h.

In the case where the first electrodes are anodes and the secondelectrode is a cathode, the first EL layer 103 e corresponds to thehole-injection layer 114 and the hole-transport layer 115 in FIG. 5B,the second EL layer 103 f corresponds to the first light-emitting layer116 d-1 in FIG. 5B, the third EL layer 103 g corresponds to the secondlight-emitting layer 116 d-2 in FIG. 5B, and the fourth EL layer 103 hcorresponds to the electron-transport layer 117 and theelectron-injection layer 118 in FIG. 5B. That is, the EL layer with thefifth structure has a structure similar to that of the EL layer 103 d inFIG. 5B, and the EL layer with the sixth structure has a structuresimilar to that of the EL layer 103 a in FIG. 5C.

The second EL layer 103 f contains an organic compound that emits bluefluorescence as a light-emitting material, and the third EL layer 103 gcontains an organic compound that emits yellow phosphorescence as alight-emitting material. The second EL layer 103 f and the third ELlayer 103 g each contain a first organic compound as a host material, inaddition to their respective light-emitting materials. Furthermore, thesecond EL layer 103 f and the third EL layer 103 g each contain a secondorganic compound as well, and it is preferable that the first organiccompound and the second organic compound form an exciplex and energytransfer occur from the exciplex to the light-emitting materials. Inaddition, the emission spectrum of the exciplex and the absorption bandof the light-emitting material on the longest wavelength side preferablyoverlap with each other, which enables energy transfer with favorableefficiency.

In the light-emitting device with this structure, it is preferable thatthe second EL layer 103 f and the third EL layer 103 g be each a layerin which the electron-transport property is higher than thehole-transport property. With such a structure, only blue fluorescencecan be obtained from the first light-emitting element and the secondlight-emitting element, and only yellow phosphorescence can be obtainedfrom the third light-emitting element. Note that in the case where thefirst electrodes are cathodes and the second electrode is an anode, thefirst EL layer 103 e corresponds to the electron-transport layer 117 andthe electron-injection layer 118 in FIG. 5B, the fourth EL layer 103 hcorresponds to the hole-injection layer 114 and the hole-transport layer115 in FIG. 5B, and it is preferable that the second EL layer 103 f andthe third EL layer 103 g be each a layer in which the hole-transportproperty is higher than the electron-transport property because of thereason similar to the above.

Although the second EL layer 103 f in FIG. 3C is formed before the thirdEL layer 103 g is formed, the third EL layer 103 g may be formed beforethe second EL layer 103 f is formed. In that case, it is preferable thatthe second EL layer 103 f and the third EL layer 103 g be each a layerin which the hole-transport property is higher than theelectron-transport property. In the case where the first electrode isthe cathode and the second electrode is the anode, it is preferable thatthe second EL layer 103 f and the third EL layer 103 g be each a layerin which the electron-transport property is higher than thehole-transport property.

Blue light can be obtained from the first light-emitting element. Whenlight emitted from the second light-emitting element enters the colorconversion layer 106G, green light can be obtained from the colorconversion layer 106G. When light emitted from the third light-emittingelement enters the color conversion layer 106R, red light can beobtained from the color conversion layer 106R. Note that light emittedfrom the first light-emitting element may be extracted outside thelight-emitting device through a color filter. Without a color filter,light can be obtained with high efficiency. Emitted through a colorfilter, light can be obtained with high color purity.

Here, the external quantum efficiency of each pixel in thelight-emitting device having the above structure and the externalquantum efficiency of each pixel in a light-emitting device having astructure different from the above will be considered. Note that thecarrier balance, exciton generation probability, and the like inlight-emitting elements used in the light-emitting devices are assumedto be similar.

First, the external quantum efficiency of each pixel in thelight-emitting device having a structure different from the above willbe calculated. The structures of the first and third light-emittingelements in the light-emitting device are similar to the structures ofthe light-emitting elements in the light-emitting device shown in FIG.3C. Although the second light-emitting element in FIG. 3C has the ELlayer with the fifth structure, the second light-emitting element inthis light-emitting device has the EL layer with the sixth structure.

In order to efficiently obtain red, green, and blue colors with thelight-emitting elements having such structures, in general, the use oflight-emitting materials that emit light having intensity at thewavelengths corresponding to the colors is effective. In view ofpracticality and efficiency, a blue fluorescent material, a redphosphorescent material, and a green phosphorescent material are oftenused. It is preferable that the blue fluorescent material be used forthe second EL layer 103 f, and the red phosphorescent material and thegreen phosphorescent material be used for the third EL layer 103 g. Withsuch a structure, light in which red light and green light aresynthesized is obtained from the second light-emitting element and thethird light-emitting element. In the second pixel, light is extractedoutside the light-emitting device through a green color filter, wherebygreen light emission can be obtained. In the third pixel, light isextracted outside the light-emitting device through a red color filter,whereby red light emission can be obtained.

Here, supposing that excitons are divided between the red phosphorescentmaterial and the green phosphorescent material half and half (1:1) inthe third EL layer, the external quantum efficiency of the blue pixel is25×χ_(A) % (in the case where a color filter is not used; it is25×χ_(CF) % in the case where a color filter is used), and the externalquantum efficiency of the green pixel and that of the red pixel are each50×χ_(CF) % (with color filters).

Next, the light-emitting device having the structure shown in FIG. 3Cwill be considered. The external quantum efficiency of the blue pixel is25×χ_(A) % (in the case where a color filter is not used; it is25×χ_(CF) % in the case where a color filter is used), the externalquantum efficiency of the green pixel is 25×χ_(CC) %, and the externalquantum efficiency of the red pixel is 100×χ_(CC) %. In this way, theuse of the structure of one embodiment of the present invention canprovide a light-emitting device with the external quantum efficiency ofthe red pixel higher than the external quantum efficiency of the redpixel in the conventional light-emitting device.

Here, the external quantum efficiency of the red pixel with thestructure of this embodiment is 100×χ_(CC) %, whereas that with theconventional structure is 50×χ_(CF) %, which means that the externalquantum efficiency of the red pixel with the structure of thisembodiment is expected to be twice that with the conventional structure,in the case where the transmittance of the color filter and the PLquantum yield of the color conversion layer are the same. Accordingly,as long as the PL quantum yield of the color conversion layer is greaterthan or equal to 50% of the transmittance of the color filter, a redpixel with the external quantum efficiency higher than that of theconventional red pixel can be obtained, and power consumption of thelight-emitting device can be reduced.

As shown in FIG. 4C, a fourth light-emitting element that constitutes ayellow pixel may be added to the structure shown in FIG. 3C. The fourthlight-emitting element includes the EL layer with the sixth structurebetween a first electrode 102Y and the second electrode 104. Theexternal quantum efficiency of the yellow pixel is 100×χ_(CF) % in thecase where light emitted from the fourth light-emitting element isextracted outside the light-emitting device through a color filter 107Y,or 100×χ_(A) % in the case where a color filter is not provided.

The light-emitting device having such a structure can express an imagewith four colors, i.e., red, green, blue, and yellow, and is excellentin color reproducibility. In addition, since yellow light has a highluminosity factor, power consumption can be reduced.

Note that in the case where the structure shown in FIG. 4C is employed,white light can be expressed only with red, blue, and yellow light, andthus the efficiency of green light hardly affects the power consumption.Accordingly, even when the efficiency of the green pixel is reduced, redlight emission is comparable to that of a conventional light-emittingelement and a highly efficient light-emitting device can be obtained aslong as the PL quantum yield of the color conversion layer 106R, whichis a first color conversion layer provided in the red pixel, is greaterthan or equal to 50% of the transmittance of a red color filter.

Only one selective deposition step that uses a mask can bring theseeffects to the light-emitting device with the structure of thisembodiment.

<Conversion from Single Element of Blue Fluorescence and Single Elementof Yellow Phosphorescence (One Selective Deposition Step Using Mask) 2>

FIG. 3D shows a light-emitting device of one embodiment of the presentinvention using a single element of blue fluorescence and a singleelement of yellow phosphorescence. As with the light-emitting deviceshown in FIG. 3A, the light-emitting device includes at least a firstlight-emitting element, a second light-emitting element, and a thirdlight-emitting element. A substrate 100, a sealing substrate 101, firstelectrodes 102B, 102G, and 102R, a second electrode 104, a black matrix105, a color conversion layer 106G, and a color conversion layer 106Rare also similar to those of the light-emitting device shown in FIG. 3A;therefore, the description is omitted here.

In the light-emitting device shown in FIG. 3D, the first light-emittingelement and the second light-emitting element include an EL layer with aseventh structure, and the third light-emitting element includes an ELlayer with an eighth structure.

The EL layer with the seventh structure is a stack including a first ELlayer 103 i, a second EL layer 103 j, and a fourth EL layer 103 m. TheEL layer with the eighth structure is a stack including the first ELlayer 103 i, the second EL layer 103 j, a third EL layer 103 k, and thefourth EL layer 103 m.

In the case where the first electrodes are anodes and the secondelectrode is a cathode, the first EL layer 103 i corresponds to thehole-injection layer 114 and the hole-transport layer 115 in FIG. 5B,the second EL layer 103 j corresponds to the first light-emitting layer116 d-1 in FIG. 5B, the third EL layer 103 k corresponds to the secondlight-emitting layer 116 d-2 in FIG. 5B, and the fourth EL layer 103 mcorresponds to the electron-transport layer 117 and theelectron-injection layer 118 in FIG. 5B. That is, the EL layer with theseventh structure has a structure similar to that of the EL layer 103 ain FIG. 5C, and the EL layer with the eighth structure has a structuresimilar to that of the EL layer 103 d in FIG. 5B.

The second EL layer 103 j contains an organic compound that emits bluefluorescence as a light-emitting material, and the third EL layer 103 kcontains an organic compound that emits yellow phosphorescence as alight-emitting material. The second EL layer 103 j and the third ELlayer 103 k each contain a first organic compound as a host material, inaddition to the light-emitting material. Furthermore, the second ELlayer 103 j and the third EL layer 103 k each contain a second organiccompound as well, and it is preferable that the first organic compoundand the second organic compound form an exciplex and energy transferoccur from the exciplex to the light-emitting material. In addition, theemission spectrum of the exciplex and the absorption band of thelight-emitting material on the longest wavelength side preferablyoverlap with each other, which enables energy transfer with favorableefficiency.

In the light-emitting device with this structure, it is preferable thatthe second EL layer 103 j and the third EL layer 103 k be each a layerin which the hole-transport property is higher than theelectron-transport property. With such a structure, only bluefluorescence can be obtained from the first light-emitting element andthe second light-emitting element, and only yellow phosphorescence canbe obtained from the third light-emitting element. Note that in the casewhere the first electrodes are cathodes and the second electrode is ananode, the first EL layer 103 i corresponds to the electron-transportlayer 117 and the electron-injection layer 118 in FIG. 5B, the fourth ELlayer 103 m corresponds to the hole-injection layer 114 and thehole-transport layer 115 in FIG. 5B, and it is preferable that thesecond EL layer 103 j and the third EL layer 103 k be each a layer inwhich the electron-transport property is higher than the hole-transportproperty because of the reason similar to the above.

Although the second EL layer 103 j in FIG. 3D is formed before the thirdEL layer 103 k is formed, the third EL layer 103 k may be formed beforethe second EL layer 103 j is formed. In that case, it is preferable thatthe second EL layer 103 j and the third EL layer 103 k be each a layerin which the hole-transport property is higher than theelectron-transport property. In the case where the first electrode isthe cathode and the second electrode is the anode, it is preferable thatthe second EL layer 103 j and the third EL layer 103 k be each a layerin which the electron-transport property is higher than thehole-transport property.

Blue light can be obtained from the first light-emitting element. Whenlight emitted from the second light-emitting element enters the colorconversion layer 106G, green light can be obtained from the colorconversion layer 106G. When light emitted from the third light-emittingelement enters the color conversion layer 106R, red light can beobtained from the color conversion layer 106R. Light emitted from thefirst light-emitting element may be extracted outside the light-emittingdevice through a color filter. Without a color filter, light can beobtained with high efficiency. Emitted through a color filter, light canbe obtained with high color purity.

Here, the external quantum efficiency of each pixel in thelight-emitting device having the above structure and the externalquantum efficiency of each pixel in a light-emitting device having astructure different from the above will be considered. Note that thecarrier balance, exciton generation probability, and the like inlight-emitting elements used in the light-emitting devices are assumedto be similar.

First, the external quantum efficiency of each pixel in thelight-emitting device having a structure different from the above willbe calculated. The structures of the first and third light-emittingelements in the light-emitting device are similar to the structures ofthe light-emitting elements in the light-emitting device shown in FIG.3D. Although the second light-emitting element in FIG. 3D has the ELlayer with the seventh structure, the second light-emitting element inthis light-emitting device has the EL layer with the eighth structure.

In order to efficiently obtain red, green, and blue colors with thelight-emitting device having such a structure, in general, the use oflight-emitting materials having respective light emission wavelengths iseffective. In view of the practicality and efficiency, a bluefluorescent material, a red phosphorescent material, and a greenphosphorescent material are often used. In the light-emitting devicehere, a blue fluorescent material is used for the second EL layer 103 j,and a red phosphorescent material and a green phosphorescent materialare used for the third EL layer 103 k.

Since the third EL layer 103 k in the EL layer with the eighth structurecontains the red and green phosphorescent materials, light in which redlight and green light are synthesized is obtained from the second andthird light-emitting elements. Therefore, light from the secondlight-emitting element is extracted outside the light-emitting devicethrough a green color filter, whereby green light emission can beobtained, and light from the third light-emitting element is extractedoutside the light-emitting device through a red color filter, wherebyred light emission can be obtained.

In the light-emitting device having such a structure, supposing thatexcitons are divided between the red phosphorescent material and thegreen phosphorescent material half and half (1:1) in the third EL layer103 k, the external quantum efficiency of the blue pixel is 25×χ_(A) %(in the case where a color filter is not used; it is 25×χ_(CF) % in thecase where a color filter is used), and the external quantum efficiencyof the green pixel and that of the red pixel are each 50×χ_(CF) %.

Next, the light-emitting device having the structure shown in FIG. 3Dwill be considered. The external quantum efficiency of the blue pixel is25×χ_(A) % (in the case where a color filter is not used; it is25×χ_(CF) % in the case where a color filter is used), the externalquantum efficiency of the green pixel is 25×χ_(CC) %, and the externalquantum efficiency of the red pixel is 100×χ_(CC) %. In this way, theuse of the structure of one embodiment of the present invention canprovide a light-emitting device with favorable external quantumefficiency of the red pixel.

Here, the external quantum efficiency of the red pixel with thestructure of this embodiment is 100×χ_(CC) %, whereas that with theconventional structure is 50×χ_(CF) %, which means that the externalquantum efficiency of the red pixel with the structure of thisembodiment e is expected to be twice that with the conventionalstructure, in the case where the transmittance of the color filter andthe PL quantum yield of the color conversion layer are the same.Accordingly, as long as the PL quantum yield of the color conversionlayer is greater than or equal to 50% of the transmittance of the colorfilter, a red pixel with the external quantum efficiency higher thanthat of the conventional red pixel can be obtained, and powerconsumption of the light-emitting device can be reduced.

As shown in FIG. 4D, a fourth light-emitting element that constitutes ayellow pixel may be added to the structure shown in FIG. 3D. The fourthlight-emitting element includes the EL layer with the eighth structurebetween a first electrode 102Y and the second electrode 104. Theexternal quantum efficiency of the yellow pixel is 100×χ_(CF) % in thecase where light emitted from the fourth light-emitting element isextracted outside the light-emitting device through a color filter 107Y,or 100×χ_(A) % in the case where a color filter is not provided.

The light-emitting device having such a structure can express an imagewith four colors, i.e., red, green, blue, and yellow, and is excellentin color reproducibility. In addition, since yellow light has a highluminosity factor, power consumption can be reduced.

Note that in the case where the structure shown in FIG. 4D is employed,white light can be expressed only with red, blue, and yellow light, andthus the efficiency of green light hardly affects the power consumption.Accordingly, even when the efficiency of the green pixel is reduced,blue light emission and red light emission are comparable to those of aconventional light-emitting element and a highly efficientlight-emitting device can be obtained as long as the PL quantum yield ofthe color conversion layer 106R, which is a first color conversion layerprovided in the red pixel, is greater than or equal to 50% of thetransmittance of a red color filter.

Only one selective deposition step that uses a mask can bring theseeffects to the light-emitting device with the structure of thisembodiment.

For each of the color conversion layers 106R, 106G, and 106Y used in theabove-described light-emitting devices, any color conversion layer maybe used as long as it can convert light with a desired wavelength intolight with a desired wavelength with desired efficiency. The typicalexamples include a color conversion layer using a fluorescent pigmentand a color conversion layer using quantum dots. A color conversionlayer using quantum dots is easily used because it can convert lightwith a wide range of wavelength. In addition, the spectrum of the lightconverted by a color conversion layer using quantum dots is sharp;therefore, light with high color purity can be obtained and alight-emitting device with excellent color reproducibility can beprovided.

<Light-Emitting Element>

Next, an example of a light-emitting element which is one embodiment ofthe present invention will be described in detail below with referenceto FIGS. 5A to 5C.

In this embodiment, the light-emitting element includes a pair ofelectrodes, i.e., a first electrode 102 and a second electrode 104, andan EL layer 103 (or an EL layer 103 d or an EL layer 103 a) providedbetween the first electrode 102 and the second electrode 104. Note thatthe first electrode 102 functions as an anode and that the secondelectrode 104 functions as a cathode.

Since the first electrode 102 functions as the anode, the firstelectrode 102 is preferably formed using any of metals, alloys,electrically conductive compounds with a high work function(specifically, a work function of 4.0 eV or more), mixtures thereof, andthe like. Specific examples include indium oxide-tin oxide (ITO: indiumtin oxide), indium oxide-tin oxide containing silicon or silicon oxide,indium oxide-zinc oxide, and indium oxide containing tungsten oxide andzinc oxide (IWZO). Such conductive metal oxide films are usually formedby a sputtering method, but may be formed by application of a sol-gelmethod or the like. In an example of the formation method, indiumoxide-zinc oxide is deposited by a sputtering method using a targetobtained by adding 1 wt % to 20 wt % of zinc oxide to indium oxide.Further, a film of indium oxide containing tungsten oxide and zinc oxide(IWZO) can be formed by a sputtering method using a target in whichtungsten oxide and zinc oxide are added to indium oxide at 0.5 wt % to 5wt % and 0.1 wt % to 1 wt %, respectively. Alternatively, gold (Au),platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum(Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), nitride of ametal material (e.g., titanium nitride), or the like can be used.Graphene can also be used. Note that when a composite material describedlater is used for a layer which is in contact with the first electrode102 in the EL layer 103, an electrode material can be selectedregardless of its work function.

The EL layer 103 (or the EL layer 103 d or the EL layer 103 a) has astacked layer structure, and the combination of a hole-injection layer,a hole-transport layer, a light-emitting layer, an electron-transportlayer, an electron-injection layer, a carrier-blocking layer, anintermediate layer, and the like can be included therein as appropriate.In this embodiment, the basic structure of the EL layer 103 (or the ELlayer 103 d or the EL layer 103 a) in which the hole-injection layer114, the hole-transport layer 115, the light-emitting layer 116, theelectron-transport layer 117, and the electron-injection layer 118 arestacked in this order over the first electrode 102 will be described.Specific examples of the materials forming the layers are given below.

The hole-injection layer 114 is a layer that contains a substance havinga high hole-injection property. As the substance having a highhole-injection property, for example, molybdenum oxide, vanadium oxide,ruthenium oxide, tungsten oxide, manganese oxide, or the like can beused. Alternatively, the hole-injection layer 114 can be formed using aphthalocyanine-based compound such as phthalocyanine (abbreviation:H₂Pc) or copper phthalocyanine (abbreviation: CuPc), an aromatic aminecompound such as4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB) orN,N′-bis{4-[bis(3-methylphenyl)amino]phenyl}-diphenyl-(1,1′-biphenyl)-4,4′-diamine(abbreviation: DNTPD), a high molecular compound such aspoly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid)(abbreviation: PEDOT/PSS), or the like.

Alternatively, a composite material in which a substance having ahole-transport property contains a substance having an acceptor propertycan be used for the hole-injection layer 114. Note that the use of sucha substance having a hole-transport property which contains a substancehaving an acceptor property enables selection of a material used to forman electrode regardless of its work function. In other words, besides amaterial having a high work function, a material having a low workfunction can also be used for the first electrode 102. As the substancehaving an acceptor property,7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ), chloranil, and the like can be given. In addition, transitionmetal oxides can be given. Moreover, an oxide of metals belonging toGroups 4 to 8 of the periodic table can be used. Specifically, it ispreferable to use vanadium oxide, niobium oxide, tantalum oxide,chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, andrhenium oxide because of their high electron accepting properties. Inparticular, molybdenum oxide is more preferable because of its stabilityin the atmosphere, low hygroscopic property, and easiness of handling.

As the substance having a hole-transport property that is used for thecomposite material, any of a variety of organic compounds such asaromatic amine compounds, carbazole derivatives, aromatic hydrocarbons,and high molecular compounds (e.g., oligomers, dendrimers, or polymers)can be used. The organic compound used for the composite material ispreferably an organic compound having a high hole-transport property.Specifically, use of a substance having a hole mobility of greater thanor equal to 10⁻⁶ cm²/(V·s) is preferable. Organic compounds that can beused as the substance having a hole-transport property in the compositematerial are specifically given below.

As the aromatic amine compound, for example, there areN,N′-di(p-tolyl)-N,N′-diphenyl-p-phenylenediamine (abbreviation:DTDPPA); 4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl(abbreviation: DPAB);N,N′-bis{4-[bis(3-methylphenyl)amino]phenyl}-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine(abbreviation: DNTPD);1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B); and the like.

The carbazole derivative that can be used for the composite material isspecifically3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2),3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1), or the like.

Other examples of the carbazole derivatives which can be used for thecomposite material include 4,4′-di(N-carbazolyl)biphenyl (abbreviation:CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB),9-[4-(10-phenyl-9-anthryl)phenyl]-9-H-carbazole (abbreviation: CzPA),and 1,4-bis[4-(N-carbazolyl)phenyl]2,3,5,6-tetraphenylbenzene.

Examples of the aromatic hydrocarbons each of which can be used for thecomposite material include 2-tert-butyl-9,10-di(2-naphthyl)anthracene(abbreviation: t-BuDNA), 2-tert-butyl-9,10-di(1-naphthyl)anthracene,9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA),2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA),9,10-di(2-naphthyl)anthracene (abbreviation: DNA),9,10-diphenylanthracene (abbreviation: DPAnth), 2-tert-butylanthracene(abbreviation: t-BuAnth), 9,10-bis(4-methyl-1-naphthyl)anthracene(abbreviation: DMNA),2-tert-butyl-9,10-bis[2-(1-naphthyl)phenyl]anthracene,9,10-bis[2-(1-naphthyl)phenyl]anthracene,2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene,2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9′-bianthryl,10,10′-diphenyl-9,9′-bianthryl,10,10′-bis(2-phenylphenyl)-9,9′-bianthryl,10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl, anthracene,tetracene, rubrene, perylene, 2,5,8,11-tetra(tert-butyl)perylene, andthe like. Besides, pentacene, coronene, or the like can also be used. Asthese aromatic hydrocarbons given here, it is preferable that anaromatic hydrocarbon having a hole mobility of 1×10⁻⁶ cm²/Vs or more andhaving 14 to 42 carbon atoms be used.

The aromatic hydrocarbons each of which can be used for the compositematerial may have a vinyl skeleton. As aromatic hydrocarbon having avinyl group, the following is given, for example:4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi);9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation: DPVPA);and the like.

Moreover, a high molecular compound such as poly(N-vinylcarbazole)(abbreviation: PVK), poly(-vinyltriphenylamine) (abbreviation: PVTPA),poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](abbreviation: PTPDMA), or poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine (abbreviation:Poly-TPD) can also be used.

By providing a hole-injection layer, a high hole-injection property canbe achieved to allow a light-emitting element to be driven at a lowvoltage.

The hole-transport layer 115 is a layer that contains a substance havinga hole-transport property. Examples of the substance having ahole-transport property are aromatic amine compounds such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine(abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA),4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB), 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: BPAFLP), and the like. The substances mentioned here havehigh hole-transport properties and are mainly ones that have a holemobility of 10⁻⁶ cm²/Vs or more. An organic compound given as an exampleof the substance having a hole-transport property in the compositematerial described above can also be used for the hole-transport layer115. Moreover, a high molecular compound such as poly(N-vinylcarbazole)(abbreviation: PVK) and poly(-vinyltriphenylamine) (abbreviation: PVTPA)can also be used. Note that the layer that contains a substance having ahole-transport property is not limited to a single layer, and may be astack of two or more layers including any of the above substances.

The electron-transport layer 117 is a layer containing a substancehaving an electron-transport property. The materials having anelectron-transport property or having an anthracene skeleton, which aredescribed above as materials for the host material, can be used.

Between the electron-transport layer and the light-emitting layer, alayer that controls transport of electron carriers may be provided. Thisis a layer formed by addition of a small amount of a substance having ahigh electron-trapping property to a material having a highelectron-transport property described above, and the layer is capable ofadjusting carrier balance by suppressing transfer of electron carriers.Such a structure is very effective in preventing a problem (such as areduction in element lifetime) caused when electrons pass through thelight-emitting layer.

In addition, an electron-injection layer 118 may be provided between theelectron-transport layer 117 and the second electrode 104, in contactwith the second electrode 104. For the electron-injection layer 118, analkali metal, an alkaline earth metal, or a compound thereof such aslithium fluoride (LiF), cesium fluoride (CsF), or calcium fluoride(CaF₂) can be used. For example, a layer that is formed using asubstance having an electron-transport property and contains an alkalimetal, an alkaline earth metal, or a compound thereof can be used. Anelectride may also be used for the electron-injection layer 118.Examples of the electride include a substance in which electrons areadded at high concentration to calcium oxide-aluminum oxide. Note thatit is preferable to use the layer formed of a substance having anelectron-transport property in which an alkali metal or an alkalineearth metal is mixed as the electron injection layer 118 becauseelectrons can be efficiently injected from the second electrode 104.

For the second electrode 104, any of metals, alloys, electricallyconductive compounds, and mixtures thereof which have a low workfunction (specifically, a work function of 3.8 eV or less) or the likecan be used. Specific examples of such a cathode material are elementsbelonging to Groups 1 and 2 of the periodic table, such as alkali metals(e.g., lithium (Li) and cesium (Cs)), magnesium (Mg), calcium (Ca), andstrontium (Sr), alloys thereof (e.g., MgAg and AlLi), rare earth metalssuch as europium (Eu) and ytterbium (Yb), alloys thereof, and the like.However, when the electron-injection layer is provided between thesecond electrode 104 and the electron-transport layer, for the secondelectrode 104, any of a variety of conductive materials such as Al, Ag,ITO, or indium oxide-tin oxide containing silicon or silicon oxide canbe used regardless of the work function. These conductive materials canbe deposited by a sputtering method, an ink-jet method, a spin coatingmethod, or the like.

Any of various methods can be employed for forming the EL layer 103 (orthe EL layer 103 d or the EL layer 103 a) regardless of whether it is adry method or a wet method. For example, a vacuum evaporation method, anink jet method, or a spin coating method may be employed. Further, adifferent deposition method can be employed for each electrode or eachlayer.

The electrodes may be formed by a wet method using a sol-gel method, orby a wet method using paste of a metal material. Alternatively, theelectrodes may be formed by a dry method such as a sputtering method ora vacuum evaporation method.

Light emission from the light-emitting element is extracted outsidethrough one or both of the first electrode 102 and the second electrode104. Therefore, one or both of the first electrode 102 and the secondelectrode 104 are formed as light-transmitting electrodes.

<Tandem Element>

Next, an embodiment of a light-emitting element with a structure inwhich a plurality of light-emitting units are stacked (hereinafter thistype of light-emitting element is also referred to as a tandemlight-emitting element) will be described with reference to FIG. 5A.This light-emitting element includes a plurality of light-emitting unitsbetween a pair of electrodes (a first electrode 102 and a secondelectrode 104). One light-emitting unit has the same structure as the ELlayer 103 a shown in FIG. 5C. In other words, the light-emitting elementshown in FIG. 5C includes one light-emitting unit while thelight-emitting element shown in FIG. 5A includes a plurality oflight-emitting units.

In FIG. 5A, the EL layer 103 including a stack of the firstlight-emitting unit 103 b, the intermediate layer 109 that correspondsto a charge generation layer, and the second light-emitting unit 103 cis formed between the first electrode 102 and the second electrode 104.One of the first light-emitting unit 103 b and the second light-emittingunit 103 c is a unit that emits blue fluorescence, and the other is aunit that emits green or yellow phosphorescence. Light in which bluefluorescence and green or yellow phosphorescence are synthesized isobtained from the EL layer 103.

The tandem element has a structure in which light-emitting units eachcorresponding to the EL layer 103 a are connected in series with theintermediate layer 109 positioned therebetween. Thus, a fluorescentlayer and a phosphorescent layer can be separated from each other, andboth fluorescence and phosphorescence can be obtained easily from onelight-emitting element.

The intermediate layer 109 includes a composite material of an organiccompound and a metal oxide. As this composite material of an organiccompound and a metal oxide, the composite material that can be used forthe hole-injection layer 114 can be used. Since the composite materialof an organic compound and a metal oxide is superior incarrier-injecting property and carrier-transporting property,low-voltage driving or low-current driving can be achieved. Note thatwhen a surface of a light-emitting unit on the anode side is in contactwith the intermediate layer, the intermediate layer can also serve as ahole-injection layer of the light-emitting unit; thus, a hole-injectionlayer does not need to be formed in the light-emitting unit.

Note that the intermediate layer 109 may be formed by stacking a layercontaining the above composite material and a layer containing anothermaterial. For example, a layer containing the above composite materialand a layer containing a compound with a high electron-transportproperty and a compound selected from the compounds with an electrondonating property may be stacked. Alternatively, a layer containing acomposite material of an organic compound and a metal oxide and atransparent conductive film may be stacked.

An electron-injection buffer layer may be provided between theintermediate layer 109 and the light-emitting unit on the anode side ofthe intermediate layer. The electron-injection buffer layer is a stackof a very thin film of an alkali metal and an electron-relay layercontaining a substance having an electron-transport property. The verythin film of the alkali metal corresponds to the electron-injectionlayer 118 and has a function of lowering an electron-injection barrier.The electron-relay layer has a function of preventing an interactionbetween the film of the alkali metal and the intermediate layer andsmoothly transferring electrons. The LUMO level of the substance havingan electron-transport property which is contained in the electron-relaylayer is set to be between the LUMO level of a substance having anacceptor property in the intermediate layer 109 and the LUMO level of asubstance contained in a layer in contact with the electron-injectionbuffer layer in the light-emitting unit on the anode side. As a specificvalue of the energy level, the LUMO level of the substance having anelectron-transport property that is contained in the electron-relaylayer is preferably greater than or equal to −5.0 eV, more preferablygreater than or equal to −5.0 eV and less than or equal to −3.0 eV. Notethat as the substance having an electron-transport property that iscontained in the electron-relay layer, a metal complex having ametal-oxygen bond and an aromatic ligand or a phthalocyanine-basedmaterial is preferably used. In that case, the film of the alkali metalof the electron-injection buffer layer serves as the electron-injectionlayer in the light-emitting unit on the anode side; thus, theelectron-injection layer does not need to be formed over thelight-emitting unit.

In any event, the intermediate layer 109 interposed between the firstlight-emitting unit 103 b and the second light-emitting unit 103 c isacceptable as long as it injects electrons to one of the light-emittingunits and injects holes to the other light-emitting unit when a voltageis applied to the first electrode 102 and the second electrode 104.

<Fluorescent/Phosphorescent Single Element>

Next, a fluorescent/phosphorescent single element with onelight-emitting unit including both a fluorescent layer and aphosphorescent layer will be described with reference to FIG. 5B. Alight-emitting element shown in FIG. 5B has a structure in which twolight-emitting layers (a first light-emitting layer 116 d-1 and a secondlight-emitting layer 116 d-2) are adjacent to each other in the EL layer103 d.

One of the first light-emitting layer 116 d-1 and the secondlight-emitting layer 116 d-2 emits blue fluorescence and the other emitsgreen or yellow phosphorescence. Light in which blue fluorescence andgreen or yellow phosphorescence are synthesized is obtained from the ELlayer 103 d.

The first light-emitting layer 116 d-1 or the second light-emittinglayer 116 d-2, which is a phosphorescent layer, contains a first organiccompound, a second organic compound, and a phosphorescent material, andit is preferable that the first organic compound and the second organiccompound form an exciplex and energy transfer occur from the exciplex tothe phosphorescent material. With such a structure, phosphorescence isnot quenched even when the fluorescent layer and the phosphorescentlayer are adjacent to each other, and fluorescence and phosphorescencecan be obtained efficiently at the same time.

When a fluorescent layer and a phosphorescent layer are included in thesame EL layer to emit light, the triplet excitation energy of thephosphorescent layer is generally transferred to a host materialoccupying a large part of the fluorescent layer. This causes asignificant reduction in emission efficiency. The reason is as follows:since a substance having a condensed aromatic ring (especially, acondensed aromatic hydrocarbon ring) skeleton, which is typified byanthracene that has a low triplet level, is generally used as a hostmaterial, triplet excitation energy generated in the phosphorescentlayer is transferred to the host material in the fluorescent layer,which results in non-radiative decay. At present, it is difficult toobtain a desired emission wavelength and favorable elementcharacteristics or reliability without using a substance having acondensed aromatic ring skeleton in the fluorescent layer; thus, thestructure in which the fluorescent layer and the phosphorescent layerare included in the same EL layer makes it difficult to obtain alight-emitting element having favorable characteristics.

Since a triplet excited state has a long relaxation time, the diffusionlength of an exciton is long, many of the excitons generated in thephosphorescent layer are transferred to the fluorescent layer because ofdiffusion, and non-radiative decay of the excitons is caused. Thisfurther reduces the emission efficiency of the phosphorescent layer.

In a light-emitting element of this embodiment, the first organiccompound and the second organic compound form an exciplex in thephosphorescent layer, and the triplet excitation energy is transferredfrom the exciplex to the phosphorescent substance, so that lightemission can be obtained. This structure can solve the above-describedproblems.

An exciplex is an excited state formed from two kinds of substances. Thetwo kinds of substances that have formed the exciplex return to a groundstate by emitting light and serve as the original two kinds ofsubstances. In other words, an exciplex itself does not have a groundstate, and energy transfer between exciplexes or energy transfer to anexciplex from another substance is unlikely to occur accordingly inprinciple.

Most excitons in the phosphorescent layer exist as exciplexes.Furthermore, the singlet-excitation energy of the exciplex is smallerthan that of the first organic compound and that of the second organiccompound. When the first organic compound and the second organiccompound are selected such that the triplet-excitation energy of theexciplex is smaller than that of the first organic compound or that ofthe second organic compound, energy transfer hardly occurs from theexciplex to the first organic compound and the second organic compound.In addition, since energy transfer among exciplex hardly occurs asdescribed above, almost all of excitation energy of the exciplex istransferred to the phosphorescent substance and converted into lightemission. Accordingly, diffusion of excitons in the phosphorescent layerhardly occurs. As a result, both fluorescence and phosphorescence can beobtained from one EL layer.

Here, in the case where the fluorescent layer and the phosphorescentlayer are formed in contact with each other, energy transfer (inparticular, triplet energy transfer) can occur from the exciplex to thehost material in the fluorescent layer at the interface. However,diffusion of the excitons in the phosphorescent layer hardly occurs asdescribed above; thus, energy transfer from the exciplex to the hostmaterial in the fluorescent layer occurs in a very limited area (i.e.,the interface between the fluorescent layer and the phosphorescentlayer), and large loss of the excitation energy does not occur.Therefore, the fluorescent layer and the phosphorescent layer need notnecessarily be in contact with each other, and even if they are contactwith each other, both fluorescence and phosphorescence can be obtainedwith high efficiency. Note that a separation layer with a thickness ofless than or equal to 20 nm may be provided between the fluorescentlayer and the phosphorescent layer. The provision of the separationlayer can suppress energy transfer at the interface between thefluorescent layer and the phosphorescent layer, whereby light emissioncan be obtained with higher efficiency. It is preferable that theseparation layer be greater than or equal to 1 nm and less than or equalto 10 nm in thickness. In addition, it is preferable that the separationlayer include the first organic compound and the second organic compoundthat are also included in the phosphorescent layer, in which case theeffect of suppressing the transfer of excitation energy is increased.

The materials included in the light-emitting layer 116, the firstlight-emitting layer 116 d-1, and the second light-emitting layer 116d-2 will be described below.

Examples of the fluorescent substances include substances which exhibitblue light emission (emission wavelength: 400 nm to 480 nm) such asN,N′-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine(abbreviation: YGA2S),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA),4-(9H-carbazol-9-yl)-4′-(9,10-diphenyl-2-anthryl)triphenylamine(abbreviation: 2YGAPPA),N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: PCAPA),4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPA),4-[4-(10-phenyl-9-anthryl)phenyl]-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPBA), perylene, 2,5,8,11-tetra(tert-butyl)perylene(abbreviation: TBP),N,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N′-diphenylpyrene-1,6-diamine(abbreviation: 1,6FLPAPrn), andN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn). Condensed aromatic diamine compoundstypified by pyrenediamine compounds such as 1,6FLPAPrn and1,6mMemFLPAPrn are particularly preferable because of their highhole-trapping properties, high emission efficiency, and highreliability.

Examples of materials that can be used as the phosphorescent substanceare as follows.

Examples of the compound that mainly emits green phosphorescence includeorganometallic iridium complexes having pyrimidine skeletons, such astris(4-methyl-6-phenylpyrimidinato)iridium(III) (abbreviation:Ir(mppm)₃), tris(4-t-butyl-6-phenylpyrimidinato)iridium(III)(abbreviation: Ir(tBuppm)₃),(acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III)(abbreviation: Ir(mppm)₂(acac)),(acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)(abbreviation: Ir(tBuppm)₂(acac)), and(acetylacetonato)bis[6-(2-norbornyl)-4-phenylpyrimidinato]iridium(III)(abbreviation: Ir(nbppm)₂(acac)); organometallic iridium complexeshaving pyridine skeletons, such astris(2-phenylpyridinato-N,C^(2′))iridium(III) (abbreviation: Ir(ppy)₃),and bis(2-phenylpyridinato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(ppy)₂(acac)); and a rare earth metal complex such astris(acetylacetonato) (monophenanthroline)terbium(III) (abbreviation:Tb(acac)₃(Phen)). Note that an organometallic iridium complex having apyrimidine skeleton has distinctively high reliability and emissionefficiency and thus is especially preferable.

Examples of the compound that mainly emits yellow phosphorescenceinclude organometallic iridium complexes having pyrimidine skeletons,such as(acetylacetonato)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidinato]iridium(III)(abbreviation: Ir(mpmppm)₂(acac)),(acetylacetonato)bis{4,6-dimethyl-2-[6-(2,6-dimethylphenyl)-4-pyrimidinyl-κN3]phenyl-κC}iridium(III)(abbreviation: Ir(dmppm-dmp)₂(acac)), and(acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III)(abbreviation: Ir(dppm)₂(acac)); organometallic iridium complexes havingpyrazine skeletons, such as(acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)(abbreviation: Ir(mppr-Me)₂(acac)) and(acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III)(abbreviation: Ir(mppr-iPr)₂(acac)); organometallic iridium complexeshaving pyridine skeletons, such astris(2-phenylquinolinato-N,C^(2′))iridium(III) (abbreviation: Ir(pq)₃),bis(2-phenylquinolinato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(pq)₂(acac)), bis(benzo[h]quinolinato)iridium(III)acetylacetonate (abbreviation: [Ir(bzq)₂(acac)]), andbis{2-[4′-(perfluorophenyl)phenyl]pyridinato-N,C^(2′)}iridium(III)acetylacetonate (abbreviation: Ir(p-PF-ph)₂(acac)); andbis(2-phenylbenzothiazolato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(bt)₂(acac)). Note that an organometallic iridiumcomplex having a pyrimidine skeleton has distinctively high reliabilityand emission efficiency and thus is especially preferable.

As a host material, various carrier-transport materials, such as amaterial having an electron-transport property or a material having ahole-transport property can be used. The host material in thephosphorescent layer preferably includes two kinds of substances, i.e.,a first organic compound and a second organic compound. Furthermore, acombination of the first organic compound and the second organiccompound preferably forms an exciplex. In addition, it is preferablethat one of the first organic compound and the second organic compoundhave an electron-transport property and the other have a hole-transportproperty, because such a structure is advantageous when forming anexciplex.

Furthermore, when a combination of these materials is selected so as toform an exciplex that exhibits light emission whose wavelength overlapsthe wavelength of a lowest-energy-side absorption band of thefluorescent substance or the phosphorescent substance, energy istransferred smoothly and light emission can be obtained efficiently.Such a combination is preferable in that drive voltage can be reduced.

Examples of the material having an electron-transport property are ametal complex such as bis(10-hydroxybenzo[h]quinolinato)beryllium(II)(abbreviation: BeBq₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III)(abbreviation: BAlq), bis(8-quinolinolato)zinc(II) (abbreviation: Znq),bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO), orbis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ); aheterocyclic compound having a polyazole skeleton such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ),1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation:CO11), 2,2′,2″-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole)(abbreviation: TPBI), or2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole(abbreviation: mDBTBIm-II); a heterocyclic compound having a diazineskeleton, such as2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-II), 2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II),2-[3′-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mCzBPDBq), 4,6-bis[3-(phenanthren-9-yl)phenyl]pyrimidine(abbreviation: 4,6mPnP2Pm), or4,6-bis[3-(4-dibenzothienyl)phenyl]pyrimidine (abbreviation:4,6mDBTP2Pm-II); and a heterocyclic compound having a pyridine skeleton,such as 3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (abbreviation:35DCzPPy) or 1,3,5-tri[3-(3-pyridyl)-phenyl]benzene (abbreviation:TmPyPB). Among the above materials, a heterocyclic compound having adiazine skeleton and a heterocyclic compound having a pyridine skeletonhave high reliability and are thus preferable. Specifically, aheterocyclic compound having a diazine (pyrimidine or pyrazine) skeletonhas a high electron-transport property and contributes to a reduction indrive voltage.

Examples of the material having a hole-transport property include acompound having an aromatic amine skeleton, such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD),4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB), 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: BPAFLP), 4-phenyl-3′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: mBPAFLP),4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation:PCBA1BP), 4,4′-diphenyl-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBBi1BP),4-(1-naphthyl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBANB),4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBNBB),9,9-dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]fluoren-2-amine(abbreviation: PCBAF), orN-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]spiro-9,9′-bifluoren-2-amine(abbreviation: PCBASF); a compound having a carbazole skeleton, such as1,3-bis(N-carbazolyl)benzene (abbreviation: mCP),4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP),3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviation: CzTP), or3,3′-bis(9-phenyl-9H-carbazole) (abbreviation: PCCP); a compound havinga thiophene skeleton such as4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation:DBT3P-II),2,8-diphenyl-4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene(abbreviation: DBTFLP-III), or4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene(abbreviation: DBTFLP-IV); and a compound having a furan skeleton, suchas 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzofuran) (abbreviation:DBF3P-II) or4-{3-[3-(9-phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran(abbreviation: mmDBFFLBi-II). Among the above materials, a compoundhaving an aromatic amine skeleton and a compound having a carbazoleskeleton are preferable because these compounds are highly reliable,have high hole-transport properties, and contribute to a reduction indrive voltage. Hole-transport materials can be selected from a varietyof substances as well as from the hole-transport materials given above.

Note that the host material may be a mixture of a plurality of kinds ofsubstances, and in the case of using a mixed host material, it ispreferable to mix a material having an electron-transport property witha material having a hole-transport property. By mixing the materialhaving an electron-transport property with the material with ahole-transport property, the transport property of the light-emittinglayer 116, the first light-emitting layer 116 d-1, and the secondlight-emitting layer 116 d-2 can be easily adjusted and a recombinationregion can be easily controlled. The ratio of the content of thematerial having a hole-transport property to the content of the materialhaving an electron-transport property may be 1:9 to 9:1.

As the host material in the fluorescent layer, materials having ananthracene skeleton such as9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation:PCzPA), 3-[4-(1-naphthyl)-phenyl]-9-phenyl-9H-carbazole (abbreviation:PCPN), 9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation:CzPA), 7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole(abbreviation: cgDBCzPA),6-[3-(9,10-diphenyl-2-anthryl)phenyl]-benzo[b]naphtho[1,2-d]furan(abbreviation: 2mBnfPPA), and9-phenyl-10-{4-(9-phenyl-9H-fluoren-9-yl)biphenyl-4′-yl} anthracene(abbreviation: FLPPA) are particularly preferable. The use of asubstance having an anthracene skeleton as the host material makes itpossible to obtain a light-emitting layer with high emission efficiencyand high durability. In particular, CzPA, cgDBCzPA, 2mBnfPPA, and PCzPAare preferable choices because of their excellent characteristics.

The light-emitting layer 116, the first light-emitting layer 116 d-1,and the second light-emitting layer 116 d-2 having the above-describedstructure can be formed by co-evaporation by a vacuum evaporationmethod, or an inkjet method, a spin coating method, a dip coatingmethod, or the like using a mixed solution.

<Micro Optical Resonator (Microcavity) Structure>

A light-emitting element with a microcavity structure is formed with theuse of a reflective electrode and a semi-transmissive andsemi-reflective electrode as the pair of electrodes. The reflectiveelectrode and the semi-transmissive and semi-reflective electrodecorrespond to the first electrode and the second electrode. At least anEL layer is provided between the reflective electrode and thesemi-transmissive and semi-reflective electrode, and the EL layerincludes at least a light-emitting layer serving as a light-emittingregion.

Note that such a structure can be effectively used particularly whenobtaining green light emission with a light-emitting device using bluefluorescence and yellow phosphorescence.

In order to obtain green light emission with the light-emitting deviceusing blue fluorescence and yellow phosphorescence, which is oneembodiment of the present invention, blue fluorescence needs to beconverted into green light with a color conversion layer. At that time,the color purity of green light may deteriorate if yellow light ismixed. Although yellow light emission may be cut with the use of a colorfilter, amplifying blue light emission and attenuating yellow lightemission with the use of a resonant structure is preferable becauseenergy loss is relatively small.

Light emitted in all directions from the light-emitting layer includedin the EL layer is reflected and resonated by the reflective electrodeand the semi-transmissive and semi-reflective electrode. Note that thereflective electrode is formed using a conductive material havingreflectivity, and a film whose visible light reflectivity is 40% to100%, preferably 70% to 100%, and whose resistivity is 1×10⁻² Ωcm orlower is used. In addition, the semi-transmissive and semi-reflectiveelectrode is formed using a conductive material having reflectivity anda light-transmitting property, and a film whose visible lightreflectivity is 20% to 80%, preferably 40% to 70%, and whose resistivityis 1×10⁻² Ωcm or lower is used.

In the light-emitting element, by changing thicknesses of thetransparent conductive film, the composite material, thecarrier-transport material, and the like, the optical path lengthbetween the reflective electrode and the semi-transmissive andsemi-reflective electrode can be changed. Thus, light with a wavelengththat is resonated between the reflective electrode and thesemi-transmissive and semi-reflective electrode can be intensified whilelight with a wavelength that is not resonated therebetween can beattenuated.

Note that light that is reflected back by the reflective electrode(first reflected light) considerably interferes with light that directlyenters the semi-transmissive and semi-reflective electrode from thelight-emitting layer (first incident light). For this reason, theoptical path length between the reflective electrode and thelight-emitting layer is preferably adjusted to (2n−1)λ/4 (n is a naturalnumber of 1 or larger and λ is a wavelength of light to be amplified).By adjusting the optical path length, the phases of the first reflectedlight and the first incident light can be aligned with each other andthe light emitted from the light-emitting layer can be furtheramplified.

Note that in the above structure, the EL layer may be formed oflight-emitting layers or may be a single light-emitting layer. Thetandem light-emitting element described above may be combined with theEL layers; for example, a light-emitting element may have a structure inwhich a plurality of EL layers is provided, a charge-generation layer isprovided between the EL layers, and each EL layer is formed oflight-emitting layers or a single light-emitting layer.

With the microcavity structure, emission intensity with a specificwavelength in the front direction can be increased, whereby powerconsumption can be reduced. In particular, a light-emitting element thatuses the 1,6-bis(diphenylamino)pyrene derivative, which has a narrowhalf width of an emission spectrum and a sharp spectrum, as an emissioncenter substance can have excellent emission efficiency because themicrocavity structure brings a significant light emission amplificationeffect.

<Light-Emitting Device>

A light-emitting device of one embodiment of the present invention willbe described with reference to FIGS. 6A and 6B. Note that FIG. 6A is atop view of the light-emitting device and FIG. 6B is a cross-sectionalview taken along the lines A-B and C-D in FIG. 6A. This light-emittingdevice includes a driver circuit portion (source line driver circuit)601, a pixel portion 602, and a driver circuit portion (gate line drivercircuit) 603, which are to control light emission of a light-emittingelement and illustrated with dotted lines. A reference numeral 604denotes a sealing substrate; 605, a sealant; and a portion surrounded bythe sealant 605 is a space 607.

A reference numeral 608 denotes a wiring for transmitting signals to beinput to the source line driver circuit 601 and the gate line drivercircuit 603 and receiving signals such as a video signal, a clocksignal, a start signal, and a reset signal from a flexible printedcircuit (FPC) 609 serving as an external input terminal. Although onlythe FPC is shown here, the FPC may be provided with a printed wiringboard (PWB). The light emitting device in this specification includesnot only a main body of the light emitting device but also the lightemitting device with an FPC or a PWB attached.

Next, a cross-sectional structure is described with reference to FIG.6B. The driver circuit portion and the pixel portion are formed over anelement substrate 610; FIG. 6B shows the source line driver circuit 601,which is a driver circuit portion, and one of the pixels in the pixelportion 602.

As the source line driver circuit 601, a CMOS circuit in which ann-channel FET 623 and a p-channel FET 624 are combined is formed. Thedriver circuit may be formed with various types of circuits, such asCMOS circuits, PMOS circuits, or NMOS circuits. A driver integrationtype in which a driver circuit is formed over a substrate is describedin this embodiment, but it is not necessarily required and a drivercircuit can be formed outside a substrate, not over the substrate.

The pixel portion 602 includes a plurality of pixels including aswitching FET 611, a current controlling FET 612, and a first electrode613 electrically connected to a drain of the current controlling FET612. One embodiment of the present invention is not limited to thestructure. The pixel portion 602 may include three or more FETs and acapacitor in combination.

The kind and crystallinity of a semiconductor used for the FETs is notparticularly limited; an amorphous semiconductor or a crystallinesemiconductor may be used. Examples of the semiconductor used for theFETs include Group 13 semiconductors (e.g., gallium), Group 14semiconductors (e.g., silicon), compound semiconductors, oxidesemiconductors, and organic semiconductors materials. Oxidesemiconductors are particularly preferable. Examples of the oxidesemiconductor include an In—Ga oxide and an In-M-Zn oxide (M is Al, Ga,Y, Zr, La, Ce, or Nd). Note that an oxide semiconductor that has anenergy gap of 2 eV or more, preferably 2.5 eV or more, furtherpreferably 3 eV or more is preferably used for a transistor, in whichcase the off-state current of the transistors can be reduced.

An insulator 614 is formed to cover an edge of the first electrode 613.In this embodiment, the insulator 614 can be formed using a positivephotosensitive acrylic resin film

The insulator 614 is formed to have a curved surface with curvature atan upper edge or a lower edge thereof in order to obtain favorablecoverage. For example, in the case where positive photosensitive acrylicis used for a material of the insulator 614, only the upper end portionof the insulator 614 preferably has a curved surface with a curvatureradius (0.2 μm to 3 μm). As the insulator 614, either a negativephotosensitive resin or a positive photosensitive resin can be used.

An EL layer 616 and a second electrode 617 are formed over the firstelectrode 613. The first electrode 613, the EL layer 616, and the secondelectrode 617 correspond to the first electrode 102, the EL layer 103(or the EL layer 103 d or the EL layer 103 a), and the second electrode104, which are described with reference to FIGS. 5A to 5C, respectively.

By attaching the sealing substrate 604 to the element substrate 610 withthe sealant 605, a light emitting element 618 is provided in the space607 surrounded by the element substrate 610, the sealing substrate 604,and the sealant 605. The space 607 is filled with a filler, there is acase where the space 607 is filled with the sealant 605 or filled withan inert gas (nitrogen, argon, or the like). It is preferable that thesealing substrate be provided with a recessed portion and a drying agent625 be provided in the recessed portion, in which case deterioration dueto influence of moisture can be suppressed.

An epoxy-based resin or glass frit is preferably used for the sealant605. The material preferably allows as little moisture and oxygen aspossible to penetrate. As the element substrate 610 and the sealingsubstrate 604, a glass substrate, a quartz substrate, or a plasticsubstrate formed of fiber reinforced plastic (FRP), poly(vinyl fluoride)(PVF), polyester, or acrylic can be used.

Note that in this specification and the like, a transistor or alight-emitting element can be formed using any of a variety ofsubstrates, for example. The type of a substrate is not limited to acertain type. As the substrate, a semiconductor substrate (e.g., asingle crystal substrate or a silicon substrate), an SOI substrate, aglass substrate, a quartz substrate, a plastic substrate, a metalsubstrate, a stainless steel substrate, a substrate including stainlesssteel foil, a tungsten substrate, a substrate including tungsten foil, aflexible substrate, an attachment film, paper including a fibrousmaterial, a base material film, or the like can be used, for example. Asan example of a glass substrate, a barium borosilicate glass substrate,an aluminoborosilicate glass substrate, a soda lime glass substrate, orthe like can be given. Examples of the flexible substrate, theattachment film, the base film, and the like are substrates of plasticstypified by polyethylene terephthalate (PET), polyethylene naphthalate(PEN), and polyether sulfone (PES). Other examples are substrates ofsynthetic resins such as acrylic. Other examples are polypropylene,polyester, polyvinyl fluoride, polyvinyl chloride, and the like. Otherexamples are polyamide, polyimide, aramid, epoxy, an inorganic vapordeposition film, paper, and the like. Specifically, the use ofsemiconductor substrates, single crystal substrates, SOI substrates, orthe like enables the manufacture of small-sized transistors with a smallvariation in characteristics, size, shape, or the like and with highcurrent capability. A circuit using such transistors achieves lowerpower consumption of the circuit or higher integration of the circuit.

Alternatively, a flexible substrate may be used as the substrate suchthat the transistor and the light-emitting element may be provideddirectly on the flexible substrate. Still alternatively, a separationlayer may be provided between the substrate and the transistor andbetween the substrate and the light-emitting element. The separationlayer can be used when part or the whole of a semiconductor deviceformed over the separation layer is separated from the substrate andtransferred onto another substrate. In such a case, the transistor canbe transferred to a substrate having low heat resistance or a flexiblesubstrate as well. For the above separation layer, a stack includinginorganic films, which are a tungsten film and a silicon oxide film, oran organic resin film of polyimide or the like formed over a substratecan be used, for example.

In other words, after the transistor and the light-emitting element isformed using a substrate, the transistor and the light-emitting elementmay be transferred to another substrate. Examples of a substrate towhich a transistor or a light-emitting element is transferred include,in addition to the above-described substrates over which transistors canbe formed, a paper substrate, a cellophane substrate, an aramid filmsubstrate, a polyimide film substrate, a stone substrate, a woodsubstrate, a cloth substrate (including a natural fiber (e.g., silk,cotton, or hemp), a synthetic fiber (e.g., nylon, polyurethane, orpolyester), a regenerated fiber (e.g., acetate, cupra, rayon, orregenerated polyester), or the like), a leather substrate, and a rubbersubstrate. When such a substrate is used, a transistor with excellentproperties or a transistor with low power consumption can be formed, adevice with high durability, high heat resistance can be provided, orreduction in weight or thickness can be achieved.

FIGS. 7A and 7B show examples of a light-emitting device of oneembodiment of the invention. In FIG. 7A, a substrate 1001, a baseinsulating film 1002, a gate insulating film 1003, gate electrodes 1006,1007, and 1008, a first interlayer insulating film 1020, a secondinterlayer insulating film 1021, a peripheral portion 1042, a pixelportion 1040, a driver circuit portion 1041, first electrodes 1024Y,1024R, 1024G, and 1024B of light-emitting elements, a partition wall1025, an EL layer 1028, a second electrode 1029 of the light-emittingelements, a sealing substrate 1031, a sealant 1032, and the like areshown. A structure that emits light in which blue fluorescence and greenor yellow phosphorescence are synthesized is assumed as the EL layer,but one embodiment of the present invention is not limited thereto.

In FIG. 7A, a red color conversion layer 1034R, a green color conversionlayer 1034G, a blue color filter layer 1034B, and a yellow colorconversion layer (in the case where blue fluorescence and greenphosphorescence are used) or a yellow color filter layer (in the casewhere blue fluorescence and yellow phosphorescence are used) 1034Y areprovided on a transparent base material 1033. Further, a black layer(black matrix) 1035 may be provided. The transparent base material 1033provided with the color filter layer, color conversion layers, and theblack layer is positioned and fixed to the substrate 1001. Note that thecolor filter layer, the color conversion layers, and the black layer maybe covered with an overcoat layer 1036.

FIG. 7B shows an example in which the color filter layer and the colorconversion layers are formed between the gate insulating film 1003 andthe first interlayer insulating film 1020. As in the structure, thecolor filter layer and the color conversion layers may be providedbetween the substrate 1001 and the sealing substrate 1031.

The above-described light-emitting device is a light-emitting devicehaving a structure in which light is extracted from the substrate 1001side where the FETs are formed (a bottom emission structure), but may bea light-emitting device having a structure in which light is extractedfrom the sealing substrate 1031 side (a top emission structure). FIG. 8is a cross-sectional view of a light-emitting device having a topemission structure. In this case, as the substrate 1001, a substratethat does not transmit light can be used. The process up to the step offorming a connection electrode which connects the FET and the anode ofthe light-emitting element is performed in a manner similar to that ofthe light-emitting device having a bottom emission structure. Then, athird interlayer insulating film 1037 is formed to cover an electrode1022. This insulating film may function for planarization. The thirdinterlayer insulating film 1037 can be formed by using a materialsimilar to that of the second interlayer insulating film, or can beformed by using any other known materials.

The first electrodes 1024Y, 1024R, 1024G, and 1024B of thelight-emitting elements each serve as an anode here, but may serve as acathode. Further, in the case of a light-emitting device having a topemission structure as shown in FIG. 8 , the first electrodes arepreferably reflective electrodes. The EL layer 1028 is formed to have astructure similar to the structure of the EL layer 103, the EL layer 103d, and the EL layer 103 a in FIGS. 5A, 5B, and 5C, respectively, and anelement structure with which white light emission can be obtained isemployed.

For the top emission structure as shown in FIG. 8 , sealing with thesealing substrate 1031 provided with the color conversion layers and thecolor filter layers is possible. The black layer (black matrix) 1035 maybe provided on the sealing substrate 1031 so as to be located betweenthe pixels. The color filter layers, the color conversion layers, andblack layers (black matrix) may be covered with an overcoat layer 1036.Note that a light-transmitting substrate is used as the sealingsubstrate 1031.

Although an example in which full color display is performed using fourcolors of red, green, blue, and yellow is shown here, there is noparticular limitation and full color display using three colors of red,green, and blue or four colors of red, green, blue, and white may beperformed.

FIGS. 9A and 9B illustrate a passive matrix light-emitting device whichis one embodiment of the present invention. FIG. 9A is a perspectiveview showing the light-emitting device, and FIG. 9B is a cross-sectionalview of FIG. 9A taken along a line X-Y. In FIGS. 9A and 9B, an EL layer955 is provided between an electrode 952 and an electrode 956 over asubstrate 951. End portions of the electrode 952 are covered by aninsulating layer 953. In addition, a partition layer 954 is providedover the insulating layer 953. A side wall of the partition layer 954slopes so that a distance between one side wall and the other side wallbecomes narrow toward a substrate surface. In other words, a crosssection in the minor axis of the partition layer 954 is a trapezoidalshape of which the lower base (the side which is in the same directionas the plane direction of the insulating layer 953 and in contact withthe insulating layer 953) is shorter than the upper base (the side whichis in the same direction as the plane direction of the insulating layer953 and not in contact with the insulating layer 953). The provision ofthe partition layer 954 in this manner can prevent the light-emittingelement from being defective due to static electricity or the like.

Since many minute light-emitting elements arranged in a matrix can eachbe controlled with the FETs formed in the pixel portion, theabove-described light-emitting device can be suitably used as a displaydevice for displaying images.

<Electronic Device>

Examples of an electronic device that is one embodiment of the presentinvention will be described. Examples of the electronic devices are atelevision device (also referred to as a television or a televisionreceiver), a monitor of a computer or the like, a camera such as adigital camera or a digital video camera, a digital photo frame, amobile phone (also referred to as a mobile telephone or a mobile phonedevice), a portable game console, a portable information terminal, anaudio reproducing device, a large-sized game machine such as a pachinkomachine, and the like. Specific examples of these electronic deviceswill be given below.

FIG. 10A shows an example of a television set. In the television device,a display portion 7103 is incorporated in a housing 7101. In addition,here, the housing 7101 is supported by a stand 7105. Images can bedisplayed on the display portion 7103, and in the display portion 7103,light-emitting elements are arranged in a matrix.

The television device can be operated with an operation switch of thehousing 7101 or a separate remote controller 7110. With operation keys7109 of the remote controller 7110, channels and volume can becontrolled and images displayed on the display portion 7103 can becontrolled. Furthermore, the remote controller 7110 may be provided witha display portion 7107 for displaying data output from the remotecontroller 7110.

Note that the television set is provided with a receiver, a modem, andthe like. With the use of the receiver, general television broadcastingcan be received. Moreover, when the television set is connected to acommunication network with or without wires via the modem, one-way (froma sender to a receiver) or two-way (between a sender and a receiver orbetween receivers) information communication can be performed.

FIG. 10B1 shows a computer, which includes a main body 7201, a housing7202, a display portion 7203, a keyboard 7204, an external connectionport 7205, a pointing device 7206, and the like. Note that this computeris manufactured by using light-emitting elements arranged in a matrix inthe display portion 7203. The computer shown in FIG. 10B1 may have astructure shown in FIG. 10B2. The computer shown in FIG. 10B2 isprovided with a second display portion 7210 instead of the keyboard 7204and the pointing device 7206. The second display portion 7210 is a touchscreen, and input can be performed by operation of display for input onthe second display portion 7210 with a finger or a dedicated pen. Thesecond display portion 7210 can also display images other than thedisplay for input. The display portion 7203 may be also a touch screen.Connecting the two screens with a hinge can prevent troubles; forexample, the screens can be prevented from being cracked or broken whilethe computer is being stored or carried.

FIGS. 10C and 10D show an example of a portable information terminal.The portable information terminal is provided with a display portion7402 incorporated in a housing 7401, an operation button 7403, anexternal connection port 7404, a speaker 7405, a microphone 7406, andthe like. Note that the portable information terminal has the displayportion 7402 including light-emitting elements arranged in a matrix.

Information can be input to the portable information terminal shown inFIGS. 10C and 10D by touching the display portion 7402 with a finger orthe like. In this case, operations such as making a call and creating ane-mail can be performed by touching the display portion 7402 with afinger or the like.

There are mainly three screen modes of the display portion 7402. Thefirst mode is a display mode mainly for displaying an image. The secondmode is an input mode mainly for inputting data such as characters. Thethird mode is a display-and-input mode in which two modes of the displaymode and the input mode are combined.

For example, in the case of making a call or creating e-mail, acharacter input mode mainly for inputting characters is selected for thedisplay portion 7402 so that characters displayed on the screen can beinput. In this case, it is preferable to display a keyboard or numberbuttons on almost the entire screen of the display portion 7402.

When a detection device including a sensor for sensing inclination, suchas a gyroscope or an acceleration sensor, is provided inside theportable information terminal, display on the screen of the displayportion 7402 can be automatically changed by determining the orientationof the portable information terminal (whether the portable informationterminal is placed horizontally or vertically for a landscape mode or aportrait mode).

The screen modes are changed by touch on the display portion 7402 oroperation with the operation button 7403 of the housing 7401. The screenmodes can be switched depending on the kind of images displayed on thedisplay portion 7402. For example, when a signal of an image displayedon the display portion is a signal of moving image data, the screen modeis switched to the display mode. When the signal is a signal of textdata, the screen mode is switched to the input mode.

Moreover, in the input mode, if a signal detected by an optical sensorin the display portion 7402 is detected and the input by touch on thedisplay portion 7402 is not performed for a certain period, the screenmode may be controlled so as to be changed from the input mode to thedisplay mode.

The display portion 7402 may function as an image sensor. For example,an image of a palm print, a fingerprint, or the like is taken by touchon the display portion 7402 with the palm or the finger, wherebypersonal authentication can be performed. Further, by providing abacklight or a sensing light source that emits near-infrared light inthe display portion, an image of a finger vein, a palm vein, or the likecan be taken.

Note that in the above electronic devices, any of the structuresdescribed in this specification can be combined as appropriate.

The display portion preferably includes a light-emitting elementincluding an organic compound of one embodiment of the presentinvention. Since the light-emitting element can be a light-emittingelement with high emission efficiency, the electronic device with lowpower consumption can be obtained. In addition, the light-emittingelement can easily have high heat resistance.

An automobile which is one embodiment of the present invention is shownin FIG. 11 . In the automobile, light-emitting elements are used for awindshield and a dashboard. Display regions 5000 to 5005 are provided byusing the light-emitting elements. The light-emitting elementspreferably include the organic compound of one embodiment of the presentinvention, and can have low power consumption. This also suppressespower consumption of the display regions 5000 to 5005, showingsuitability for use in an automobile.

The display regions 5000 and 5001 are provided in the automobilewindshield including the light-emitting elements. When a first electrodeand a second electrode are formed of electrodes havinglight-transmitting properties in these light-emitting elements, what iscalled a see-through display device, through which the opposite side canbe seen, can be obtained. Such see-through light-emitting devices can beprovided even in the automobile windshield without hindering the vision.Further, for example, in the case where a transistor for driving thelight-emitting element is provided, it is preferable to use a transistorhaving a light-transmitting property, such as an organic transistorusing an organic semiconductor material or a transistor using an oxidesemiconductor.

The display region 5002 is provided in a pillar portion using alight-emitting element. The display region 5002 can compensate for theview hindered by the pillar portion by showing an image taken by animaging unit provided in the car body. Similarly, the display region5003 provided in the dashboard can compensate for the view hindered bythe car body by showing an image taken by an imaging unit provided onthe outside of the car body, which leads to elimination of blind areasand enhancement of safety. Showing an image so as to compensate for thearea which a driver cannot see makes it possible for the driver toconfirm safety easily and comfortably.

The display region 5004 and the display region 5005 can provide avariety of kinds of information such as navigation information, aspeedometer, a tachometer, a mileage, a fuel meter, a gearshiftindicator, and air-condition setting. The contents or layout of thedisplay can be changed by a user as appropriate. Note that suchinformation can also be shown by the display regions 5000 to 5003. Thedisplay regions 5000 to 5005 can also be used as lighting devices.

FIGS. 12A to 12C show a foldable portable information terminal 9310.FIG. 12A shows the portable information terminal 9310 that is opened.FIG. 12B shows the portable information terminal 9310 that is beingopened or being folded. FIG. 12C illustrates the portable informationterminal 9310 that is folded. The portable information terminal 9310 ishighly portable when folded. When the portable information terminal 9310is opened, a seamless large display region is highly browsable.

A display panel 9311 is supported by three housings 9315 joined togetherby hinges 9313. By folding the portable information terminal 9310 at aconnection portion between two housings 9315 with the hinges 9313, theportable information terminal 9310 can be reversibly changed in shapefrom an opened state to a folded state. A light-emitting device of oneembodiment of the present invention can be used for the display panel9311. A display region 9312 is a display region that is positioned at aside surface of the portable information terminal 9310 that is folded.On the display region 9312, information icons, frequently-usedapplications, file shortcuts to programs, and the like can be displayed,and confirmation of information and start of application can be smoothlyperformed.

As described above, the electronic devices can be obtained byapplication of the light-emitting device according to one embodiment ofthe present invention. Note that the light-emitting device can be usedfor electronic devices in a variety of fields without being limited tothe electronic devices described in this embodiment.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

EXPLANATION OF REFERENCE

100: substrate, 101: sealing substrate, 102: first electrode, 102R:first electrode, 102G: first electrode, 102B: first electrode, 102Y:first electrode, 102Rt: transparent conductive film, 102Gt: transparentconductive film, 102Bt: transparent conductive film, 102Yt: transparentconductive film, 103: EL layer, 103 a: EL layer, 103 b: firstlight-emitting unit, 103 c: second light-emitting unit, 103 d: EL layer,103 e: first EL layer, 103 f: second EL layer, 103 g: third EL layer,103 h: fourth EL layer, 103 i: first EL layer, 103 j: second EL layer,103 k: third EL layer, 103 m: fourth EL layer, 104: second electrode,105: black matrix, 106R: color conversion layer, 106G: color conversionlayer, 106Y: color conversion layer, 107G: color filter, 107B: colorfilter, 107Y: color filter, 109: intermediate layer, 114: hole-injectionlayer, 115: hole-transport layer, 116: light-emitting layer, 116 d-1:first light-emitting layer, 116 d-2: second light-emitting layer, 117:electron-transport layer, 118: electron-injection layer, 601: drivercircuit portion (source line driver circuit), 602: pixel portion, 603:driver circuit portion (gate line driver circuit), 604: sealingsubstrate, 605: sealant, 607: space, 608: wiring, 609: FPC (flexibleprinted circuit), 610: element substrate, 611: switching FET, 612:current controlling FET, 613: first electrode, 614: insulator, 616: ELlayer, 617: second electrode, 618: light-emitting element, 623:n-channel FET, 624: p-channel FET, 625: drying agent, 915: substrate,952: electrode, 953: insulating layer, 954: partition layer, 955: ELlayer, 956: electrode, 1001: substrate, 1002: base insulating film,1003: gate insulating film, 1006: gate electrode, 1007: gate electrode,1008: gate electrode, 1020: first interlayer insulating film, 1021:second interlayer insulating film, 1022: electrode, 1024Y: firstelectrode of light-emitting element, 1024R: first electrode oflight-emitting element, 1024G: first electrode of light-emittingelement, 1024B: first electrode of light-emitting element, 1025:partition wall, 1028: EL layer, 1029: second electrode of light-emittingelement, 1031: sealing substrate, 1032: sealant, 1033: transparent basematerial, 1034R: red color conversion layer, 1034G: green colorconversion layer, 1034B: blue color filter layer, 1034Y: yellow colorconversion layer, 1035: black layer (black matrix), 1037: thirdinterlayer insulating film, 1040: pixel portion, 1041: driver circuitportion, 1042: peripheral portion, 5000: display region, 5001: displayregion, 5002: display region, 5003: display region, 5004: displayregion, 5005: display region, 7101: housing, 7103: display portion,7105: stand, 7107: display portion, 7109: operation key, 7110: remotecontroller, 7201: main body, 7202: housing, 7203: display portion, 7204:keyboard, 7205: external connection port, 7206: pointing device, 7210:second display portion, 7301: housing, 7302: housing, 7303: connectionportion, 7304: display portion, 7305: display portion, 7306: speakerportion, 7307: recording medium insertion portion, 7308: LED lamp, 7309:operation key, 7310: connection terminal, 7311: sensor, 7401: housing,7402: display portion, 7403: operation button, 7404: external connectionport, 7405: speaker, 7406: microphone, 9310: portable informationterminal, 9311: display panel, 9312: display region, 9313: hinge, 9315:housing

This application is based on Japanese Patent Application serial no.2014-112796 filed with Japan Patent Office on May 30, 2014 and JapanesePatent Application serial no. 2014-112849 filed with Japan Patent Officeon May 30, 2014, the entire contents of which are hereby incorporated byreference.

The invention claimed is:
 1. A light-emitting device comprising: a firstlight-emitting element; a second light-emitting element; and a thirdlight-emitting element, wherein the first light-emitting element, thesecond light-emitting element, and the third light-emitting element eachcomprise an organic compound, wherein the first light-emitting element,the second light-emitting element, and the third light-emitting elementcomprise a common layer containing a light-emitting material that emitsblue fluorescence, wherein the first light-emitting element, the secondlight-emitting element, and the third light-emitting element comprise acommon layer containing a light-emitting material that emits yellowphosphorescence, wherein light emitted from the first light-emittingelement enters a first color conversion layer but does not enter a colorfilter, wherein light emitted from the second light-emitting elemententers a second color conversion layer but does not enter a colorfilter, and wherein light emitted from the third light-emitting elementdoes not enter a color conversion layer but is extracted through a firstcolor filter.
 2. The light-emitting device according to claim 1, whereinthe first color conversion layer comprises a color conversion substancethat emits green light, wherein the second color conversion layercomprises a color conversion substance that emits red light, and whereinthe first color filter transmits blue light.
 3. The light-emittingdevice according to claim 1, wherein the first to third light-emittingelements are tandem light-emitting elements.
 4. The light-emittingdevice according to claim 1, wherein the first color conversion layerand the second color conversion layer are each a color conversion layerusing quantum dots.
 5. A light-emitting device comprising: a firstlight-emitting element; a second light-emitting element; and a thirdlight-emitting element, wherein the first light-emitting element, thesecond light-emitting element, and the third light-emitting element eachcomprise an organic compound, wherein the first light-emitting element,the second light-emitting element, and the third light-emitting elementcomprise a common layer containing a light-emitting material that emitsyellow phosphorescence, wherein the first light-emitting element and thethird light-emitting element each comprise a layer containing alight-emitting material that emits blue fluorescence, wherein the secondlight-emitting element does not comprise the layer containing thelight-emitting material that emits blue fluorescence, wherein lightemitted from the first light-emitting element enters a first colorconversion layer but does not enter a color filter, wherein lightemitted from the second light-emitting element enters a second colorconversion layer but does not enter a color filter, and wherein lightemitted from the third light-emitting element is extracted withoutthrough a color conversion layer and a color filter.
 6. Thelight-emitting device according to claim 5, wherein the layer containingthe light-emitting material that emits blue fluorescence is closer to ananode than the layer containing the light-emitting material that emitsyellow phosphorescence is, and wherein both the layer containing thelight-emitting material that emits blue fluorescence and the layercontaining the light-emitting material that emits yellow phosphorescenceare layers whose electron-transporting properties are higher thanhole-transporting properties.
 7. The light-emitting device according toclaim 5, wherein the layer containing the light-emitting material thatemits blue fluorescence is closer to a cathode than the layer containingthe light-emitting material that emits yellow phosphorescence is, andwherein both the layer containing the light-emitting material that emitsblue fluorescence and the layer containing the light-emitting materialthat emits yellow phosphorescence are layers whose hole-transportingproperties are higher than electron-transporting properties.
 8. Thelight-emitting device according to claim 5, wherein a PL quantum yieldof the second color conversion layer is higher than 50%.
 9. Thelight-emitting device according to claim 5, wherein light emitted fromthe first color conversion layer is green light, and wherein lightemitted from the second color conversion layer is red light.
 10. Thelight-emitting device according to claim 5, wherein the first colorconversion layer and the second color conversion layer are each a colorconversion layer using quantum dots.
 11. A light-emitting devicecomprising: a first light-emitting element; a second light-emittingelement; and a third light-emitting element, wherein the firstlight-emitting element, the second light-emitting element, and the thirdlight-emitting element each comprise an organic compound, wherein thefirst light-emitting element, the second light-emitting element, and thethird light-emitting element comprise a common layer containing alight-emitting material that emits blue fluorescence, wherein the secondlight-emitting element comprises a layer containing a light-emittingmaterial that emits yellow phosphorescence, wherein the firstlight-emitting element and the third light-emitting element do notcomprise the layer containing the light-emitting material that emitsyellow phosphorescence, wherein light emitted from the firstlight-emitting element enters a first color conversion layer but doesnot enter a color filter, wherein light emitted from the secondlight-emitting element enters a second color conversion layer but doesnot enter a color filter, and wherein light emitted from the thirdlight-emitting element is extracted without through a color conversionlayer and a color filter.
 12. The light-emitting device according toclaim 11, wherein the layer containing the light-emitting material thatemits blue fluorescence is closer to an anode than the layer containingthe light-emitting material that emits yellow phosphorescence is, andwherein both the layer containing the light-emitting material that emitsblue fluorescence and the layer containing the light-emitting materialthat emits yellow phosphorescence are layers whose hole-transportingproperties are higher than electron-transporting properties.
 13. Thelight-emitting device according to claim 11, wherein the layercontaining the light-emitting material that emits blue fluorescence iscloser to a cathode than the layer containing the light-emittingmaterial that emits yellow phosphorescence is, and wherein both thelayer containing the light-emitting material that emits bluefluorescence and the layer containing the light-emitting material thatemits yellow phosphorescence are layers whose electron-transportingproperties are higher than hole-transporting properties.
 14. Thelight-emitting device according to claim 11, wherein a PL quantum yieldof the second color conversion layer is higher than 50%.
 15. Thelight-emitting device according to claim 11, wherein light emitted fromthe first color conversion layer is green light, and wherein lightemitted from the second color conversion layer is red light.
 16. Thelight-emitting device according to claim 11, wherein the first colorconversion layer and the second color conversion layer are each a colorconversion layer using quantum dots.